a(n) = T(2n+1,n+3), T given by A026736.

Terms

a(0) =1a(1) =7a(2) =36a(3) =166a(4) =729a(5) =3125a(6) =13229a(7) =55637a(8) =233227a(9) =976271a(10) =4085016a(11) =17096524a(12) =71590557a(13) =299993227a(14) =1258076725a(15) =5280194087a(16) =22178492943a(17) =93226087229a(18) =392144055809