my $p = 9 + # 1 digit (9 * 8) + # 2 digits (9 * 8 * 7) + # 3 digits (9 * 8 * 7 * 6) + # 4 digits (9 * 8 * 7 * 6 * 5) + # 5 digits (9 * 8 * 7 * 6 * 5 * 4) + # 6 digits (9 * 8 * 7 * 6 * 5 * 4 * 3) + # 7 digits (9 * 8 * 7 * 6 * 5 * 4 * 3 * 2) + # 8 digits (9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1); # 9 digits say $p; # = 986,409