# A259275 (b-file synthesized from sequence entry) 0 1 1 5 2 20 3 105 4 520 5 2580 6 12945 7 64680 8 323320 9 1616780 10 8083745 11 40418380 12 202092620 13 1010462480 14 5052310420 15 25261556205 16 126307777920 17 631538879180 18 3157694416720 19 15788472066780 20 78942360284720 21 394711801527505 22 1973559007551520 23 9867795037511480 24 49338975188073020