# A131448 (b-file synthesized from sequence entry) 1 1 2 2 3 2 4 24 5 40 6 144 7 5040 8 40320 9 6048 10 6048 11 19958400 12 53222400 13 53222400 14 87178291200 15 118879488000 16 5230697472000 17 8083805184000 18 3201186852864000 19 40548366802944000 20 2432902008176640000 21 17030314057236480000