# A047097 (b-file synthesized from sequence entry) 0 1 1 4 2 16 3 60 4 228 5 860 6 3267 7 12426 8 47471 9 181812 10 698512 11 2690086 12 10384712 13 40170182 14 155681112 15 604362074 16 2349783665 17 9148780570 18 35665860725 19 139202880860 20 543887439194 21 2127148912456 22 8326877989146 23 32623644335536