# A005559 (b-file synthesized from sequence entry) 1 1 2 2 3 8 4 20 5 75 6 210 7 784 8 2352 9 8820 10 27720 11 104544 12 339768 13 1288287 14 4294290 15 16359200 16 55621280 17 212751396 18 734959368 19 2821056160 20 9873696560 21 38013731756 22 134510127752 23 519227905728 24 1854385377600 25 7174705330000 26 25828939188000 27 100136810390400