Puzzle 8-13-2008

[Steven Schveighoffer]

"Wyverex" wrote
>> What is the largest prime factor of the number 600851475143 ?
>>
>
> import tango.io.Stdout;
>
> T max( T )( T a, T b) { return ( a > b ? a : b ); }
>
> void main()
> {
>   real i = 600851475143;
>   real m = 0;
>
>   real l = 2;
>   while(l*l <= i)
>   {
>     if(i%l == 0)
>     {
>      m = max(m,l);
>      Stdout(l)(" ");
>      i /= l;
>     }
>     ++l;
>   }
>   Stdout(l).newline;
>   m = max(m,l);
>   Stdout("Max: ")(cast(long)m).newline;
> }
>
> output:
> 71.00 839.00 1471.00 1472.00
> Max:1472

1472 is not prime.

Hint for doing prime stuff, don't use floating point types :)

Also, the second to last line, taking the max of l and m is questionable.

-Steve