use Math::BigInt;
@Primes = (2,3,5,7,11,13,17,19,23,29,31,37,41,
	43,47,53,59,61,67,71,73,79,83,89,97,101);
@AsciiPrimes = ((0) x 65, @Primes, (0) x 6, @Primes, (0) x 133);

print StringDif('abcdgoldfish', 'flash'),"\n";
print StringDif('lmnogoldfish', 'dish'),"\n";
print StringDif('osar', 'oar'),"\n";

sub StringDif {
	my ($StrA, $StrB) = @_;
	my $A = Math::BigInt->new(1);
	my $B = Math::BigInt->new(1);
	my $Quot, $Rem, $NewQuot, $ReturnStr;
	foreach (unpack 'C*', $StrA) {$A *= $AsciiPrimes[$_]}
	foreach (unpack 'C*', $StrB) {$B *= $AsciiPrimes[$_]}
	if ($A eq '+0' or $B eq '+0') {
		warn "Non-letter in string"; return undef
	}
	($Quot, $Rem) = Math::BigInt->new($A)->bdiv($B);
	return undef unless $Rem eq '+0';
	$ReturnStr = '';
	foreach('a'..'z') {
		do {
			($NewQuot, $Rem) = Math::BigInt->new($Quot)
				->bdiv($AsciiPrimes[ord $_]);
			if ($Rem eq '+0') {
				$ReturnStr .= $_;
				$Quot = $NewQuot
			}
		} while $Rem eq '+0' 
	}
	return $ReturnStr
}