# A002571 (b-file synthesized from sequence entry) 1 1 2 5 3 10 4 30 5 74 6 199 7 515 8 1355 9 3540 10 9276 11 24276 12 63565 13 166405 14 435665 15 1140574 16 2986074 17 7817630 18 20466835 19 53582855 20 140281751 21 367262376 22 961505400 23 2517253800 24 6590256025 25 17253514249 26 45170286749 27 118257345970