Print the nth Fibonacci number containing the nth Fibonacci number!

Question

Challenge

You must write a program that takes a positive integer n as input, and outputs the nth Fibonacci number (shortened as Fib# throughout) that contains the nth Fib# as a subtring. For the purposes of this challenge, the Fibonacci sequence begins with a 1.

Here are some examples that you can use as test cases, or as examples to clarify the challenge (for the latter, please leave a comment down below explaining what you find unclear).

n=1
Fib#s: 1
       ^1 1st Fib# that contains a 1 (1st Fib#)
Output: 1

n=2
Fib#s: 1, 1
       ^1 ^2 2nd Fib# that contains a 1 (2nd Fib#)
Output: 1

n=3
Fib#s: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233
             ^1              ^2                   ^3 3rd Fib# that contains a 2 (3rd Fib#)
Output: 233

n=4
Output: 233

n=5
Output: 6765

n=6
Output: 28657

n=7
Output: 1304969544928657

n=8
Output: 14472334024676221

n=9
Output: 23416728348467685

n=10
Fib#s: 1, ..., 34, 55, 89, ..., 63245986, 102334155, 165580141, ..., 2880067194370816120, 4660046610375530309
                   ^1                     ^2         ^3                                   ^10 10th Fib# that contains a 55 (10th Fib#)
Output: 4660046610375530309

---

As always, this is code-golf, so go for the lowest byte count possible.

If something is confusing/unclear, please leave a comment.

(This challenge is based off another challenge I posted: Print the nth prime that contains n)

Answer 1

Haskell, 85 84 bytes

EDIT:

• -1 byte: Laikoni shortened l.
• Typo (x>=s for x<=s) in explanation.

f takes an Int and returns a String.

l=0:scanl(+)1l
m=show<$>l
f n|x<-m!!n=[y|y<-x:m,or[x<=s|s<-scanr(:)""y,x++":">s]]!!n

Try it online!

How it works

• l is the infinite list of Fibonacci numbers, defined recursively as the partial sums of 0:1:l. It starts with 0 because lists are 0-indexed. m is the same list converted to strings.
• In f:
  • n is the input number, and x is the (string of the) nth Fibonacci number.
  • In the outer list comprehension, y is a Fibonacci number tested for whether it contains x as a substring. The passing ys are collected in the list and indexed with the final !!n to give the output. An extra x is prepended to the tests to save two bytes over using !!(n-1) at the end.
  • To avoid counting ys several times, the tests of each y are wrapped in or and another list comprehension.
  • In the inner list comprehension, s iterates through the suffixes of y.
  • To test whether x is a prefix of s, we check whether x<=s and x++":">s. (":" is somewhat arbitrary but needs to be larger than any numeral.)

Answer 2

Jelly, 15 14 bytes

1 byte thanks to Jonathan Allan.

0µ³,ÆḞẇ/µ³#ÆḞṪ

Try it online!

Answer 3

Python 2, 99 86 bytes

• Ørjan Johansen Saved 7 bytes: starting with b=i=x=-1 a=1 and dropping the x and
• Ørjan Johansen again saved 3 bytes: f and n==2 to f*(n>2)
• Felipe Nardi Batista saved 9 bytes: economic swap a,b=a+b,a shorthand f-=str(x)in str(a), squeezed (n<2)*f
• ovs saved 13 bytes: transition from python 3 to python 2.

f=n=input()
b=i=x=-1
a=1
while(n>2)*f:i+=1;a,b=a+b,a;x=[x,a][i==n];f-=`x`in`a`
print a

Try it online!

Explanation:

f=n=int(input())                 # f is number of required numbers

b=i=x=-1                         # i is index(counter) set at -1
                                 # In Two-sided fibonacci, fib(-1) is 1 
                                 # and b(fib before it) i.e. fib(-2) is -1
                                 # Taking advantage of all -1 values, x is 
                                 # also set to -1 so that the `if str(...`
                                 # portion does not execute until x is set a 
                                 # value(i.e. the nth fibonacci) since there 
                                 # is no way -1 will be found in the number 
                                 # (ALL HAIL to Orjan's Genius Idea of using 
                                 # two-sided fibonacci)      

a=1                              # fib(-1) is 1


while(n>2)*f:                    # no need to perform this loop for n=1 and 
                                 # n=2 and must stop when f is 0

 i+=1                            # increment counter

 b,a=a,a+b                       # this might be very familiar (fibonacci 
                                 # thing ;))                         

 x=[x,a][i==n]                   # If we have found (`i==n`) the nth 
                                 # fibonacci set x to it

 f-=`x`in`a`                     # the number with required substring is 
                                 # found, decrease value of f

print a                          # print required value

Python 3, 126 120 113 112 110 101 99 bytes

f=n=int(input())
b=i=x=-1
a=1
while(n>2)*f:i+=1;a,b=a+b,a;x=[x,a][i==n];f-=str(x)in str(a)
print(a)

Try it online!

Answer 4

Java, 118 111 bytes

i->{long n=i,p=0,q,c=1;for(;--n>0;p=c,c+=q)q=p;for(n=c;i>0;q=p,p=c,c+=q)if((""+c).contains(""+n))--i;return p;}

I keep thinking it should be possible not to duplicate the Fibonacci bit, but all my efforts somehow result in more bytes.

Thanks to Kevin for improvements... guess it shows this was my first attempt at golfing :)

Answer 5

Perl 6, 45 bytes

{my@f=0,1,*+*...*;@f.grep(/$(@f[$_])/)[$_-1]}

$_ is the argument to the function; @f is the Fibonacci sequence, lazily generated.

Answer 6

JavaScript (ES6), 96 93 92 90 86 bytes

0-indexed, with the 0th number in the sequence being 1. Craps out at 14.

f=(n,x=1,y=1)=>n?f(n-1,y,x+y):x+""
g=(n,x=y=0)=>x>n?f(y-1):g(n,x+!!f(y++).match(f(n)))

• 2 6 bytes saved thanks to Arnauld

---

Try it

f=(n,x=1,y=1)=>n?f(n-1,y,x+y):x+""
g=(n,x=y=0)=>x>n?f(y-1):g(n,x+!!f(y++).match(f(n)))
oninput=_=>o.innerText=(v=+i.value)<14?`f(${v}) = ${f(v)}\ng(${v}) = `+g(v):"Does not compute!"
o.innerText=`f(0) = ${f(i.value=0)}\ng(0) = `+g(0)

<input id=i min=0 type=number><pre id=o>

---

Explanation

Updated version to follow, when I get a minute.

f=...                   :Just the standard, recursive JS function for generating the nth Fibonacci number
g=(...)=>               :Recursive function with the following parameters.
n                       :  The input integer.
x=0                     :  Used to count the number of matches we've found.
y=0                     :  Incremented on each pass and used to generate the yth Fibonacci number.
x>n?                    :If the count of matches is greater than the input then
f(y-1)                  :    Output the y-1th Fibonacci number.
:                       :Else
g(...)                  :    Call the function again, with the following arguments.
n                       :      The input integer.
x+                      :      The total number of matches so far incremented by the result of...
RegExp(f(n)).test(f(y)) :        A RegEx test checking if the yth Fibonacci number, cast to a string, contains the nth Fibonacci number.
                        :        (returns true or false which are cast to 1 and 0 by the addition operator)
y+1                     :      The loop counter incremented by 1

Answer 7

Charcoal, 65 bytes

ＡＩθνＡνφＡ±¹βＡβιＡβξＡ¹αＷ∧›ν²φ«Ａ⁺ι¹ιＡ⁺αβχＡαβＡχαＡ⎇⁼ιναξξＡ⁻φ›№ＩαＩξ⁰φ»Ｉα

Try it online! Link to verbose code for explanation.

Answer 8

Mathematica, 85 bytes

(i=ToString;f=Fibonacci;For[n=t=0,t<#,If[i@f@n++~StringContainsQ~i@f@#,t++]];f[n-1])&

input

[10]

-4 bytes from @JungHwan Min

output

4660046610375530309

Answer 9

R, 77 72 bytes

F=gmp::fibnum;i=0;d=n=scan();while(n)if(grepl(F(d),F(i<-i+1)))n=n-1;F(i)

This makes use of the gmp library for the Fibonacci number. Fairly straight foward implementation of the question.

F=gmp::fibnum;          # Alias Fibonacci function to F
i=0;                    # intitalise counter
d=n=scan();             # get n assign to d as well
while(n)               # loop while n
  if(grepl(F(d),F(i<-i+1)))  # use grepl to determine if Fib of input is in Fib# and increment i
     n=n-1;             # decrement n
F(i)                  # output result

Some tests

> F=gmp::fibnum;i=0;d=n=scan();while(n)if(grepl(F(d),F(i<-i+1)))n=n-1;F(i)
1: 2
2: 
Read 1 item
Big Integer ('bigz') :
[1] 1
> F=gmp::fibnum;i=0;d=n=scan();while(n)if(grepl(F(d),F(i<-i+1)))n=n-1;F(i)
1: 3
2: 
Read 1 item
Big Integer ('bigz') :
[1] 233
> F=gmp::fibnum;i=0;d=n=scan();while(n)if(grepl(F(d),F(i<-i+1)))n=n-1;F(i)
1: 10
2: 
Read 1 item
Big Integer ('bigz') :
[1] 4660046610375530309
> F=gmp::fibnum;i=0;d=n=scan();while(n)if(grepl(F(d),F(i<-i+1)))n=n-1;F(i)
1: 15
2: 
Read 1 item
Big Integer ('bigz') :
[1] 1387277127804783827114186103186246392258450358171783690079918032136025225954602593712568353

Answer 10

PHP, 96 bytes

for($f=[0,1];$s<$a=$argn;$s+=$f[$a]&&strstr($f[$i],"$f[$a]")?:0)$f[]=$f[$i]+$f[++$i];echo$f[$i];

Try it online!

Answer 11

Clojure, 99 bytes

(def s(lazy-cat[0 1](map +(rest s)s)))#(nth(filter(fn[i](.contains(str i)(str(nth s %))))s)(dec %))

A basic solution, uses an infinite sequence of Fibonacci numbers s.

Answer 12

C#, 35 bytes

int u=1,b=1;for(;b<n;){b+=u;u=b-u;}

Try it

int n=int.Parse(t2.Text);int u=1,b=1;for(;b<n;){b+=u;u=b-u;t.Text+=b.ToString()+" ";}if(b==n){t.Text+="true";}

Answer 13

NewStack, 14 bytes

N∞ ḟᵢfi 'fif Ṗf⁻

The breakdown:

N∞              Add all natural numbers to the stack
   ḟᵢ           Define new function will value of input
     fi          Get the n'th Fibonacci number for ever element n
       'fif      Remove all elements that don't contain the (input)'th Fibonacci number 
           Ṗf⁻  Print the (input-1)'th element

In English: (with example of an input of 3)

N∞: Make a list of the natural numbers [1,2,3,4,5,6...]

ḟᵢ: Store the input in the variable f [1,2,3,4,5,6...]

fi: Convert the list to Fibonacci numbers [1,1,2,3,5,8...]

'fif: Keep all elements that contain the fth Fibonacci number [2,21,233...]

Ṗf⁻: Print the f-1th element (-1 due to 0-based indexing) 233

Answer 14

Japt, 16 15 bytes

_søNg)«´U}a@MgX

Try it