# A018559 (b-file synthesized from sequence entry) 1 1 2 2 3 3 4 5 5 6 6 7 7 9 8 10 9 14 10 15 11 18 12 21 13 30 14 35 15 42 16 45 17 63 18 70 19 90 20 105 21 126 22 210 23 315 24 630