# A124355 (b-file synthesized from sequence entry) 1 0 2 0 3 2 4 6 5 24 6 120 7 720 8 5040 9 40320 10 362880 11 3628800 12 39916800 13 479001600 14 6227020800 15 87178291200 16 1307674368000 17 20922789888000 18 355687428096000 19 6402373705728000 20 121645100408832000 21 2432902008176640000