my @a = qw(1 4 6 2 7 87 5 6 4 32);
my @b = qw(86 50 62 41 32);
my %primes;
map { $primes{$_}++ } map { primes($_) } @a;
map { $primes{$_}-- } map { primes($_) } @b;

sub primes {
   ... # left as an exercise for the reader
}

##</code><code>##

$result *= $_ ** $primes{$_} for keys %primes;