a(n) = binomial(n,18).

Terms

a(0) =1a(1) =19a(2) =190a(3) =1330a(4) =7315a(5) =33649a(6) =134596a(7) =480700a(8) =1562275a(9) =4686825a(10) =13123110a(11) =34597290a(12) =86493225a(13) =206253075a(14) =471435600a(15) =1037158320a(16) =2203961430a(17) =4537567650a(18) =9075135300a(19) =17672631900a(20) =33578000610a(21) =62359143990a(22) =113380261800a(23) =202112640600a(24) =353697121050a(25) =608359048206