# A007231 (b-file synthesized from sequence entry) 1 1 2 5 3 13 4 52 5 121 6 455 7 1093 8 4305 9 9841 10 36905 11 88573 12 348728 13 797161 14 2989355 15 7174453 16 28585712 17 64570081 18 242137805 19 581130733 20 2288202262