a(n) = N(5,n), where N(5,x) is the 5th Narayana polynomial.

Terms

a(0) =1a(1) =42a(2) =197a(3) =562a(4) =1257a(5) =2426a(6) =4237a(7) =6882a(8) =10577a(9) =15562a(10) =22101a(11) =30482a(12) =41017a(13) =54042a(14) =69917a(15) =89026a(16) =111777a(17) =138602a(18) =169957a(19) =206322a(20) =248201a(21) =296122a(22) =350637a(23) =412322a(24) =481777a(25) =559626a(26) =646517a(27) =743122a(28) =850137a(29) =968282