# A002750 (b-file synthesized from sequence entry) 0 1 1 4 2 15 3 76 4 373 5 2676 6 17539 7 152860 8 1383561 9 14658148 10 143131351 11 2070738924 12 24754959805 13 341745565396 14 5260157782923 15 92358395065276 16 1377499388715409 17 27622124789948100 18 476285499100204831 19 10464946811144407948 20 222724531608924013701