Am I perfect (number)?

Question

This is my first challenge!

Background

Perfect number is a positive integer, that is equal to the sum of all its divisors, except itself.
So 6 is perfect number, since 1 + 2 + 3 = 6.
On the other hand 12 is not, because 1 + 2 + 3 + 4 + 6 = 16 != 12.

Task

Your task is simple, write a program, which will, for given n, print one of these messages:

I am a perfect number, because d1 + d2 + ... + dm = s == n
I am not a perfect number, because d1 + d2 + ... + dm = s [<>] n

Where
d1, ... dm are all divisors of n except for n.
s is the sum of all divisors d1, ..., dm (again, without n).
[<>] is either < (if s < n) or > (if s > n).

Examples

For n being 6: "I am a perfect number, because 1 + 2 + 3 = 6 == 6"
For n being 12: "I am not a perfect number, because 1 + 2 + 3 + 4 + 6 = 16 > 12"
For n being 13: "I am not a perfect number, because 1 = 1 < 13"

Rules

• n is not bigger than your language's standard int.
• You can read n from standard input, from command line arguments or from a file.
• Output message has to be printed on standard output and no additional characters can appear in the output (it may have trailing whitespace or newline)
• You may not use any built-ins or library functions which would solve the task (or its main part) for you. No GetDivisors() or something like that.
• All other standard loopholes apply.

Winner

This is code-golf so shortest code in bytes wins!

Answer 1

Pyth, 81 bytes

jd[+WK-QsJf!%QTStQ"I am"" not""a perfect number, because"j" + "J\=sJ@c3"==<>"._KQ

Try it online: Demonstration or Test Suite

Explanation:

                                 implicit: Q = input number
               StQ               the range of numbers [1, 2, ..., Q-1]
          f                      filter for numbers T, which satisfy:
           !%QT                     Q mod T != 0
         J                       save this list of divisors in J
      -QsJ                       difference between Q and sum of J
     K                           save the difference in K

jd[                              put all of the following items in a list
                                 and print them joined by spaces: 
                  "I am"           * "I am"
   +WK                  " not"       + "not" if K != 0
"a perfect number, because"        * "a perfect ..."
j" + "J                            * the divisors J joined by " + "
       \=                          * "="
         sJ                        * sum of J
            c3"==<>"               * split the string "==<>" in 3 pieces:
                                        ["==", "<", ">"]
           @        ._K              and take the (sign of K)th one (modulo 3)
                       Q           * Q

Answer 2

Java, 255 270 bytes (Still FF in base 17)

class C{public static void main(String[]a){int i=new Integer(a[0]),k=0,l=0;a[0]=" ";for(;++k<i;)if(i%k<1){l+=k;a[0]+=k+" ";}}System.out.print("I am "+(l==i?"":"not ")+"a perfect number, because "+a[0].trim().replace(" "," + ")+" = "+l+(l==i?" == ":l<i?" < ":" > ")+i);}}

And a more readable version:

class C {
    public static void main(String[] a) {
        int i = new Integer(a[0]), k = 0, l = 0;
        a[0] = " ";
        for(; ++k<i ;){
            if (i % k == 0) {
                l += k;
                a[0] += k + " ";
            }
        }
        System.out.print("I am " + (l == i ? "" : "not ") + "a perfect number, because " + a[0].trim().replace(" "," + ") + " = " + l + (l == i ? " == " : l < i ? " < " : " > ") + i);
    }
}

Previously didn't work for odd numbers, so I had to tweak a few things. At least I got lucky with the byte count again. :)

Answer 3

R, 158 163 157 153 143 141 bytes

Still room to golf this I think.
Edit: Replaced if(b<n)'<'else if(b>n)'>'else'==' with c('<'[b<n],'>'[b>n],'=='[b==n]). The paste(...) is replaced with an rbind(...)[-1]. Thanks @plannapus for a couple more bytes.

n=scan();a=2:n-1;b=sum(w<-a[!n%%a]);cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)

Ungolfed

n<-scan()             # get number from stdin
w<-which(!n%%1:(n-1)) # build vector of divisors
b=sum(w)              # sum divisors
cat('I am',           # output to STDOUT with a space separator
    'not'[b!=n],      # include not if b!=n
    'a perfect number, because',
    rbind('+',w)[-1], # create a matrix with the top row as '+', remove the first element of the vector
    '=',
    b,                # the summed value
    c(                # creates a vector that contains only the required symbol and ==
        '<'[b<n],     # include < if b<n
        '>'[b>n],     # include > if b>n
        '=='
    )[1],             # take the first element 
    n                 # the original number
)

Test run

> n=scan();b=sum(w<-which(!n%%1:(n-1)));cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)
1: 6
2: 
Read 1 item
I am a perfect number, because 1 + 2 + 3 = 6 == 6
> n=scan();b=sum(w<-which(!n%%1:(n-1)));cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)
1: 12
2: 
Read 1 item
I am not a perfect number, because 1 + 2 + 3 + 4 + 6 = 16 > 12
> n=scan();b=sum(w<-which(!n%%1:(n-1)));cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)
1: 13
2: 
Read 1 item
I am not a perfect number, because 1 = 1 < 13
> 

Answer 4

Python 2, 183 173 170 bytes

b=input();c=[i for i in range(1,b)if b%i<1];d=sum(c);print'I am %sa perfect number because %s = %d %s %d'%('not '*(d!=b),' + '.join(map(str,c)),d,'=<>='[cmp(b,d)%3::3],b)

Examples:

$ python perfect_number.py <<< 6
I am a perfect number because 1 + 2 + 3 = 6 == 6
$ python perfect_number.py <<< 12
I am not a perfect number because 1 + 2 + 3 + 4 + 6 = 16 > 12
$ python perfect_number.py <<< 13
I am not a perfect number because 1 = 1 < 13
$ python perfect_number.py <<< 100
I am not a perfect number because 1 + 2 + 4 + 5 + 10 + 20 + 25 + 50 = 117 > 100
$ python perfect_number.py <<< 8128
I am a perfect number because 1 + 2 + 4 + 8 + 16 + 32 + 64 + 127 + 254 + 508 + 1016 + 2032 + 4064 = 8128 == 8128

Thanks to xnor for saving 13 bytes!

Answer 5

Julia, 161 157 bytes

n=int(ARGS[1])
d=filter(i->n%i<1,1:n-1)
s=sum(d)
print("I am ",s!=n?"not ":"","a perfect number, because ",join(d," + ")," = $s ",s<n?"<":s>n?">":"=="," $n")

Ungolfed:

# Read n as the first command line argument
n = int(ARGS[1])

# Get the divisors of n and their sum
d = filter(i -> n % i == 0, 1:n-1)
s = sum(d)

# Print to STDOUT
print("I am ",
      s != n ? "not " : "",
      "a perfect number, because ",
      join(d, " + "),
      " = $s ",
      s < n ? "<" : s > n ? ">" : "==",
      " $n")

Answer 6

CJam, 90 bytes

"I am"rd:R{R\%!},:D:+R-g:Cz" not"*" a perfect number, because "D'+*'=+D:++'=C+_'=a&+a+R+S*

For comparison, printing a single = could be achieved in 83 bytes.

Try it online in the CJam interpreter.

How it works

"I am"  e# Push that string.
rd:R    e# Read a Double from STDIN and save it in R.
{       e# Filter; for each I in [0 ... R-1]:
  R\%!  e# Push the logical NOT of (R % I).
},      e# Keep the elements such that R % I == 0.
:D      e# Save the array of divisors in D.
:+R-g   e# Add the divisors, subtract R and compute the sign of the difference.
:Cz     e# Save the sign in C and apply absolute value.
"not "* e# Repeat the string "not " that many times.

" a perfect number, because "

D'+*    e# Join the divisors, separating by plus signs.
'=+D:++ e# Append a '=' and the sum of the divisors.
'=C+    e# Add the sign to '=', pushing '<', '=' or '>'.
_'=a&   e# Intersect a copy with ['='].
+a+     e# Concatenate, wrap in array and concatenate.
        e# This appends "<", "==" or ">".
R+      e# Append the input number.
S*      e# Join, separating by spaces.

Answer 7

Lua, 244 231 bytes

Golfed:

n=io.read("*n")d={}s="1"t=1 for i=2,n-1 do if n%i==0 then table.insert(d,i)s=s.." + "..i t=t+i end end print(("I am%s a perfect number, because %s = %s"):format(t==n and""or" not", s, t..(t==n and" == "or(t>n and" > "or" < "))..n))

Ungolfed:

n=io.read("*n")
divisors={}
sequence="1"
sum=1
for i=2,n-1 do
    if n%i==0 then 
        table.insert(divisors,i)
        sequence=sequence.." + "..i
        sum=sum+i
    end
end

print(("I am%s a perfect number, because %s = %s"):format(sum==n and""or" not", sequence, sum..(sum==n and" == "or(sum>n and" > "or" < "))..n))

Answer 8

Perl, 148 Bytes

$a=<>;$_=join' + ',grep{$a%$_==0}1..$a-1;$s=eval;print"I am ".($s==$a?'':'not ')."a perfect number because $_ = $s ".(('==','>','<')[$s<=>$a])." $a"

With line breaks:

$a=<>;
$_=join' + ',grep{$a%$_==0}1..$a-1;
$s=eval;
print"I am ".($s==$a?'':'not ')."a perfect number because $_ = $s ".(('==','>','<')[$s<=>$a])." $a"

Answer 9

Ruby, 174 160 155 136 134 128 122 Bytes

n=6;a=[*1...n].reject{|t|n%t>0};b=a.inject(:+)<=>n;print"I am#{" not"*b.abs} a perfect number, because ",a*?+,"<=>"[b+1],n

Saved another 6 Bytes :)

Thanks to Tips for golfing in Ruby

Answer 10

JavaScript (ES6), 146

Using template strings, it works in Firefox and latest Chrome.

for(n=prompt(),o=t=i=1;++i<n;)n%i||(t+=i,o+=' + '+i)
alert(`I am ${t-n?'not ':''}a perfect number because ${o} = ${t} ${t<n?'<':t>n?'>':'=='} `+n)

Answer 11

C#, 252 bytes

class A{static void Main(string[]a){int i=int.Parse(a[0]);var j=Enumerable.Range(1,i-1).Where(o=>i%o==0);int k=j.Sum();Console.Write("I am "+(i!=k?"not ":"")+"a perfect number, because "+string.Join(" + ",j)+" = "+k+(k>i?" > ":k<i?" < ":" == ")+i);}}

Answer 12

Hassium, 285 Bytes

Disclaimer: Works with only the latest version of Hassium due to issues with command line args.

func main(){n=Convert.toNumber(args[0]);s=1;l="1";foreach(x in range(2,n-3)){if(n%x==0){l+=" + "+x;s+=x;}}if(s==n)println("I am a perfect number, because "+l+" = "+s+" == "+s);else {print("I am not a perfect number, because "+l+" = "+s);if(s>n)println(" > "+n);else println(" < "+n);}}

More readable version:

func main() {
    n = Convert.toNumber(args[0]);
    s = 1;
    l = "1";
    foreach(x in range(2, n - 3)) {
            if (n % x== 0) {
                    l += " + " + x;
                    s += x;
            }
    }
    if (s == n)
            println("I am a perfect number, because " + l + " = " + s + " == " + s);
    else {
            print("I am not a perfect number, because " + l + " = " + s);
            if (s > n)
                    println(" > " + n);
            else
                    println(" < " + n);
    }

}

Answer 13

MATLAB, 238

Never going to be the shortest of all languages, but here's my attempt with MATLAB:

n=input('');x=1:n-1;f=x(~rem(n,x));s=sum(f);a='not ';b=strjoin(strtrim(cellstr(num2str(f')))',' + ');if(s>n) c=' > ';elseif(s<n) c=' < ';else c=' == ';a='';end;disp(['I am ' a 'a perfect number, because ' b ' = ' num2str(s) c num2str(n)])

And this is in a slightly more readable form:

n=input();      %Read in the number using the input() function
x=1:n-1;        %All integers from 1 to n-1
f=x(~rem(n,x)); %Determine which of those numbers are divisors
s=sum(f);       %Sum all the divisors
a='not ';       %We start by assuming it is not perfect (to save some bytes)
b=strjoin(strtrim(cellstr(num2str(f')))',' + '); %Also convert the list of divisors into a string 
                                                 %where they are all separated by ' + ' signs.
%Next check if the number is >, < or == to the sum of its divisors
if(s>n)  
    c=' > ';    %If greater than, we add a ' > ' to the output string
elseif(s<n) 
    c=' < ';    %If less than, we add a ' < ' to the output string
else
    c=' == ';   %If equal, we add a ' == ' to the output string
    a='';       %If it is equal, then it is a perfect number, so clear the 'not' string
end

%Finally concatenate the output string and display the result
disp(['I am ' a 'a perfect number, because ' b ' = ' num2str(s) c num2str(n)])

I've managed to save 2 more bytes by not using a function. Instead you run the line of code and it requests the number as an input. Once run it displays the output at the end.

Answer 14

Perl 6, 138 bytes

$_=get;
my$c=$_ <=>my$s=[+] my@d=grep $_%%*,^$_;
say "I am {
    'not 'x?$c
  }a perfect number, because {
    join ' + ',@d
  } = $s {
    «> == <»[1+$c]
  } $_"

( The count ignores the newlines, and indents, because they aren't needed )

@d is the array holding the divisors.
$s holds the sum of the divisors.
$c is the value of the comparison between the input, and the sum of the divisors.
( effectively $c is one of -1,0,1, but is really one of Order::Less, Order::Same, or Order::More )

In 'not 'x?$c, ?$c in this case is effectively the same as abs $c, and x is the string repetition operator.

«> == <» is short for ( '>', '==', '<' ).
Since $c has one of -1,0,1, we have to shift it up by one to be able to use it to index into a list.

Technically this will work for numbers well above 2⁶⁴, but takes an inordinate amount of time for numbers above 2¹⁶.

Answer 15

05AB1E, 58 bytes

„I€ÜIѨ©OIÊi'€–}“€…íÀ‚³,ƒ«“®vy'+}\'=®ODI.S"==><"211S£sèIðý

Try it online or verify all test cases.

Explanation:

„I€Ü              # Push dictionary string "I am"
IѨ               # Push the divisors of the input-integer, with itself removed
   ©              # Store it in the register (without popping)
    O             # Get the sum of these divisors
     IÊi   }      # If it's not equal to the input-integer:
        '€–      '#  Push dictionary string "not"
“€…íÀ‚³,ƒ«“       # Push dictionary string "a perfect number, because"
®v   }            # Loop `y` over the divisors:
  y'+            '#  Push the divisor `y`, and the string "+" to the stack
      \           # Discard the final "+"
       '=        '# And push the string "="
®O                # Get the sum of the divisors again
  D               # Duplicate it
I.S               # Compare it to the input-integer (-1 if smaller; 0 if equal; 1 if larger)
   "==><"         # Push string "==><"
         211S£    # Split into parts of size [2,1,1]: ["==",">","<"]
              sè  # Index into it (where the -1 will wrap around to the last item)
I                 # Push the input-integer again
ðý                # Join everything on the stack by spaces
                  # (and output the result implicitly)

See this 05AB1E tip of mine (section How to use the dictionary?) to understand why „I€Ü is "I am", '€– is "not", and “€…íÀ‚³,ƒ«“ is "a perfect number, because".

Answer 16

Pyth, 84 bytes

jd+,+"I am"*.aK._-QsJf!%QTtUQ" not""a perfect number, because"+.iJm\+tJ[\=sJ@"=<>"KQ

Invalid answer, because I refuse to implement = and == in the same equation.

Answer 17

Ruby, 164 Bytes

->i{t=(1...i).select{|j|i%j==0};s=t.inject &:+;r=['==','>','<'][s<=>i];puts "I am #{'not ' if r!='=='}a perfect number, because #{t.join(' + ')} = #{s} #{r} #{i}"}

Test

irb(main):185:0> ->i{t=(1...i).select{|j|i%j==0};s=t.inject &:+;r=['==','>','<'][s<=>i];puts "I am #{'not ' if r!='=='}a perfect number, because #{t.join(' + ')} = #{s} #{r} #{i}"}.call 6
I am a perfect number, because 1 + 2 + 3 = 6 == 6

irb(main):186:0> ->i{t=(1...i).select{|j|i%j==0};s=t.inject &:+;r=['==','>','<'][s<=>i];puts "I am #{'not ' if r!='=='}a perfect number, because #{t.join(' + ')} = #{s} #{r} #{i}"}.call 12
I am not a perfect number, because 1 + 2 + 3 + 4 + 6 = 16 > 12

irb(main):187:0> ->i{t=(1...i).select{|j|i%j==0};s=t.inject &:+;r=['==','>','<'][s<=>i];puts "I am #{'not ' if r!='=='}a perfect number, because #{t.join(' + ')} = #{s} #{r} #{i}"}.call 13
I am not a perfect number, because 1 = 1 < 13

Answer 18

Emacs Lisp, 302 Bytes

(defun p(n)(let((l(remove-if-not'(lambda(x)(=(% n x)0))(number-sequence 1(- n 1)))))(setf s(apply'+ l))(format"I am%s a perfect number, because %s%s = %s %s %s"(if(= s n)""" not")(car l)(apply#'concat(mapcar'(lambda(x)(concat" + "(number-to-string x)))(cdr l)))s(if(= sum n)"=="(if(> sum n)">""<"))n)))

Ungolfed version:

(defun perfect (n)
  (let ((l (remove-if-not '(lambda (x) (= (% n x) 0))
              (number-sequence 1 (- n 1)))))
    (setf sum (apply '+ l))
    (format "I am%s a perfect number, because %s%s = %s %s %s" (if (= sum n)"" " not") (car l)
        (apply #'concat (mapcar '(lambda (x) (concat " + " (number-to-string x))) (cdr l)))
        sum (if(= sum n)
            "=="
          (if(> sum n)
              ">"
            "<"))
        n)))

Answer 19

Powershell, 164 bytes

$a=$args[0]
$b=(1..($a-1)|?{!($a%$_)})-join" + "
$c=iex $b
$d=$a.compareto($c)
"I am $("not "*!!$d)a perfect number, because $b = $c $(("==","<",">")[$d]) $a"

A few of the common and not so common PoSh tricks;

• Create the sum, then evaluate it with iex
• Compareto to index the gt, lt, eq array
• !!$d will evaluate to true == 1 for $d = 1 or -1, and false == 0 for $d = 0

Answer 20

awk, 150

n=$0{for(p=i=s=n>1;++i<n;)for(;n%i<1;p+=i++)s=s" + "i;printf"I am%s a perfect number, because "s" = "p" %s "n RS,(k=p==n)?_:" not",k?"==":p<n?"<":">"}

Wasted some bytes on making this correct for input 1. I'm not sure if that is expected.

n=$0{
    for(p=i=s=n>1;++i<n;)
        for(;n%i<1;p+=i++)s=s" + "i;
    printf "I am%s a perfect number, because "s" = "p" %s "n RS,
           (k=p==n)?_:" not",k?"==":p<n?"<":">"
}