a(n) = A001609(n)^2, where g.f. of A001609 is x*(1+3*x^2)/(1-x-x^3).

Terms

a(0) =1a(1) =1a(2) =16a(3) =25a(4) =36a(5) =100a(6) =225a(7) =441a(8) =961a(9) =2116a(10) =4489a(11) =9604a(12) =20736a(13) =44521a(14) =95481a(15) =205209a(16) =440896a(17) =946729a(18) =2033476a(19) =4368100a(20) =9381969a(21) =20151121a(22) =43283241a(23) =92968164a(24) =199685161a(25) =428904100a(26) =921243904a(27) =1978737289a(28) =4250127249a(29) =9128847025