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CREATE SCHEMA IF NOT EXISTS pwc159;
/**
testdb=> select pwc159.mobius( 5 );
mobius
--------
-1
(1 row)
*/
CREATE OR REPLACE FUNCTION
pwc159.mobius( int )
RETURNS int
AS $CODE$
my ( $n ) = @_;
# a routine to compute the prime
# factors of the given number
my $prime_factors = sub {
my ( $number ) = @_;
my %factors;
my $factor = 2;
while ( $number > 1 && $factor <= $number ) {
if ( $number % $factor == 0 ) {
$factors{ $factor }++;
$number /= $factor;
}
else {
$factor++;
}
}
return %factors;
};
my %prime_factors = $prime_factors->( $n );
# to get the unique prime factors I have to "count"
# them only once per key
my @unique_prime_factors;
my $occurrencies_prime_factors = 0;
for ( keys %prime_factors ) {
push @unique_prime_factors, $_;
$occurrencies_prime_factors += $prime_factors{ $_ };
}
return 0 if @unique_prime_factors != $occurrencies_prime_factors;
return 1 if @unique_prime_factors % 2 == 0;
return -1;
$CODE$
LANGUAGE plperl;
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