# A058540 (b-file synthesized from sequence entry) 0 0 1 1 2 3 3 9 4 36 5 144 6 651 7 3015 8 14634 9 72654 10 369063 11 1904985 12 9971889 13 52788393 14 282161025 15 1520597895 16 8253281871 17 45075359277 18 247534382298 19 1365994896264 20 7571065357620 21 42127865408028 22 235246997219400 23 1317894484506336