Code Golf: Prime Factors of a Number [closed]

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What is the shortest way, by character count, to find prime factors in any number?

Example Input: 1806046

Example Output: 2x11x11x17x439

Example Calculator

Answer 1

Euphoria: 106 characters

procedure f(atom a)atom x=2
loop do
while remainder(a,x)do
x+=1
end while
?x
a/=x
until a=1
end procedure

Answer 2

Mathematica (15 chars including brackets):

FactorInteger

Example:

FactorInteger[42]

{{2, 1}, {3, 1}, {7, 1}}

Answer 3

Python recursive solution

99 characters (including spaces) 87 characters (without spaces)

def f(n,i=2,r=""):
    while n%i<1:r+="%dx"%i;n/=i
    return f(n,i+1,r)if n>1 else r
print f(input())[:-1]

Update: A completely recursive version

def f(n,i=2,x=""): return x if n<2 else f(n,i+1,x)if n%i else f(n/i,i,x+'%dx'%i)
print f(input())[:-1]

Both versions are prone to stack overflows for all but the smallest of inputs.

Answer 4

GNU bc, 47 chars, including collecting input (need the GNU extensions for print, else and read):

x=read();for(i=2;x>1;)if(x%i){i+=1}else{x/=i;i}

If you really want the x characters in the output, it's 64 chars:

x=read();for(i=2;x>1;)if(x%i){i+=1}else{x/=i;print i;if(x>1)"x"}

Also, note that using bc allows this to process numbers of arbitrary length.

Answer 5

Best Perl answer yet - 70 characters, and no extra modules (unless you count special features of 5.10):

perl -nE'sub f{($a)=@_;$a%$_||return$_,f($a/$_)for 2..$a}$,=x;say f$_'

Doesn't work for 1 or 0, but works fine for everything else. If you don't like using say, or are using an earlier version of Perl, here's an 81 character version:

perl -ne'sub f{($a)=@_;$a%$_||return$_,f($a/$_)for 2..$a;}$,=x;$/="\n";print f$_'

Answer 6

Ruby 39B 71B (via STDIN)

#!ruby -nrmathn
p$_.to_i.prime_division.map{|d,c|[d]*c}.flatten.join"x"