X
N =  C
      Y

##</code><code>##

    X      X(x) * X(x-1) * ... * X(y+1)
N =  C  =  ----------------------------
      Y       1 * 2 * ... (x - y)

##</code><code>##

use strict;

sub xCy()
{
    my ($x, $y) = @_;
    return(0) if $x < $y;   # can not pick more number than given
    return(1) if $x == $y;  # 1 combination if X = Y

    my $diff = $x - $y;
    my $n = 1;
    for (0 .. $diff-1) { $n *= $x - $_ }
    my $m = 1;
    for (1 .. $diff) { $m *= $_ }

    return $n / $m;
}

printf "%d\n", &xCy($_, 6) for 7 .. 10;

__END__
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