# A022491 (b-file synthesized from sequence entry) 1 0 2 1 3 2 4 6 5 18 6 72 7 321 8 1680 9 9852 10 64168 11 457659 12 3543785 13 29578097 14 264623046 15 2525897073 16 25622275565 17 275257714175 18 3122190896616 19 37290114445901 20 467812869356846