# A003283 (b-file synthesized from sequence entry) 0 1 1 2 2 20 3 70 4 112 5 352 6 1232 7 22880 8 183040 9 1244672 10 30098432 11 72352 12 2472371200 13 115763200 14 441223168 15 6838959104 16 61568122880 17 745298329600 18 28321336524800 19 1103041527808 20 573581594460160 21 4275790067793920 22 49961677422592