Calculate the factorial of a number without using recursion or loops

Question

The goal of this code golf is to create a program that calculates the factorial of a positive number, without using recursion or loops. The rules:

1. Your program should prompt for input. This input will be a positive integer
2. Your program should output the factorial of the given positive integer
3. You are not allowed to use recursion or loops (including goto)
4. You are not allowed to execute an external program
5. You are not allowed to use a built-in function to calculate the factorial (including eval functions)
6. Your program MUST work without network connection

Good luck!

Answer 1

APL, 4 characters / GolfScript, 9 characters

APL:

×/⍳⎕

GolfScript:

~),1>{*}*

Answer 2

Tcl, 82

puts [lindex {1 1 2 6 24 120 720 5040 40320 362880 3628800 39916800} [gets stdin]]

No eval, no recursion, no loops. As requested. Only works with 32-Bit integers.

Answer 3

Mathematica, 32

Integrate[x^Input[]/E^x,{x,0,∞}]

I hope I did everything correctly, otherwise please correct it.
I don't even have Mathematica.

If nothing else works, use the Gamma function.

Answer 4

Mathematica 20

This should be easy to beat.

Times@@Range@Input[]

Answer 5

R - 14 characters

prod(1:scan())

Answer 6

Bash 43

Using only internal commands:

read n;echo $((`eval "echo 1 '*'{1..$n}"`))

The inside is pretty much seq -s'*' $n

Answer 7

Ruby, 25 characters

p eval [*1..gets.to_i]*?*

Answer 8

Excel Formula, 32

=PRODUCT(ROW(INDIRECT("1:"&A1)))

Enter as an array formula, and the value to be factored should be in A1

it's 34 if you have to count the {} that excel will put around the formula when successfully entered with Ctrl+Shift+Enter

Answer 9

Perl 6 (14 bytes)

I assume that reduce operator ([*]) is not a loop.

say [*] 2..get

Answer 10

Java, 500 bytes

A couple years late to the party, but I think I've captured the spirit of the question, as it uses no form of looping whatsoever. Takes the first command line argument as an integer (greater than or equal to 1), and prints out its factorial, or terminates with exception in the case of overflow. Since java integers can only hold the factorials of numbers up to 16, it just uses a switch statement with the results hard coded in ;)

public class M{public static void main(String[]args){int n=Integer.parseInt(args[0]);int r;switch(n){case(1):r=1;break;case(2):r=2;break;case(3):r=6;break;case(4):r=24;break;case(5):r=120;break;case(6):r=720;break;case(7):r=5040;break;case(8):r=40320;break;case(9):r=362880;break;case(10):r=3628800;break;case(11):r=39916800;break;case(12):r=479001600;break;case(13):r=1932053504;break;case(14):r=1278945280;break;case(15):r=2004310016;break;case(16):r=2004189184;break;default:r=1/0;}System.out.print(r);}}

EDIT - Saved 7 bytes thanks to NoOneIsHere

class M{public static void main(String[]args){int n=Integer.parseInt(args[0]);int r;switch(n){case(1):r=1;break;case(2):r=2;break;case(3):r=6;break;case(4):r=24;break;case(5):r=120;break;case(6):r=720;break;case(7):r=5040;break;case(8):r=40320;break;case(9):r=362880;break;case(10):r=3628800;break;case(11):r=39916800;break;case(12):r=479001600;break;case(13):r=1932053504;break;case(14):r=1278945280;break;case(15):r=2004310016;break;case(16):r=2004189184;break;default:r=1/0;}System.out.print(r);}}

Answer 11

TI-Basic, 9 bytes

prod(seq(I,I,1,Ans

Makes a list from 1 to the input and calculates the product.

Answer 12

Ruby: 30 26 characters

(“Translation” of David Carraher's answer.)

p [*1..gets.to_i].reduce:*

Sample run:

bash-4.1$ ruby -e 'p [*1..gets.to_i].reduce:*' <<< 5
120

bash-4.1$ ruby -e 'p [*1..gets.to_i].reduce:*' <<< 10
3628800

Answer 13

J, 14 characters

*/1+i.".1!:1[1

Answer 14

Python 3 - 77 characters

import functools
print(functools.reduce(int.__mul__,range(1,int(input())+1)))

Answer 15

Ruby, 21 characters

p eval [*?1..gets]*?*

Answer 16

Haskell - 51 characters

main=getLine >>=(print .(\n->product[1..n]). read)

From Evolution of a Haskell Programmer, the tenured professor.

Answer 17

PHP, 116

class a{function __destruct(){global $_,$x,$i,$argv;$x*=$i;if($i++<$argv[1])$_=new a;else echo$x;}}$i=$x=1;$_=new a;

No recursions, loops, range, reduce, implode, repeat, map, etc.

Answer 18

Factor, 44 bytes

[ 1 readln string>number 1 <range> product ] 

Answer 19

Julia

As a function — 12 bytes:

n->prod(1:n)

With an input prompt — 23 bytes:

prod(1:int(readline()))

By integration — 50 bytes:

n=int(readline());int(quadgk(x->x^n/e^x,0,Inf)[1])

(Not sure if the function-only form qualifies, re rule #1.)