# A002751 (b-file synthesized from sequence entry) 0 1 1 3 2 9 3 37 4 153 5 951 6 5473 7 42729 8 353937 9 3455083 10 30071001 11 426685293 12 4707929449 13 59350096287 14 882391484913 15 15177204356401 16 205119866263713 17 4040196156574419 18 64262949875511337 19 1408785031894483893 20 29514546353782633401 21 593055713389216814983