a(n) = T(n,n), array T given by A048505.

Terms

a(0) =1a(1) =5a(2) =35a(3) =160a(4) =577a(5) =1816a(6) =5245a(7) =14288a(8) =37313a(9) =94384a(10) =232861a(11) =563080a(12) =1339249a(13) =3141464a(14) =7282493a(15) =16711456a(16) =38010625a(17) =85786336a(18) =192282301a(19) =428342936a(20) =948960881a(21) =2091908680a(22) =4590665245a(23) =10032774640a(24) =21843934657a(25) =47395634576a(26) =102508789085a(27) =221056597288a(28) =475399191793