# A002490 (b-file synthesized from sequence entry) 0 1 1 0 2 2 3 1652 4 119550 5 1497328 6 16733124 7 108084480 8 588808172 9 2544811584 10 9516509988 11 31328336284 12 92876219432 13 252846150384 14 638250041288 15 1511780647680 16 3387237676950 17 7228330859840 18 14769380958438 19 29023337216604 20 55108233751768 21 101433859301088