# A074581 (b-file synthesized from sequence entry) 0 0 1 2 2 13 3 81 4 504 5 3136 6 19513 7 121415 8 755476 9 4700770 10 29249425 11 181997601 12 1132436852 13 7046319384 14 43844049029 15 272809183135 16 1697490356184 17 10562230626642 18 65720971788709 19 408933139743937 20 2544489349890656