a(n) = (1/4)*A291038(n).

Terms

a(0) =1a(1) =3a(2) =8a(3) =21a(4) =54a(5) =136a(6) =337a(7) =825a(8) =2000a(9) =4809a(10) =11484a(11) =27264a(12) =64401a(13) =151455a(14) =354808a(15) =828349a(16) =1927986a(17) =4475080a(18) =10361441a(19) =23936565a(20) =55183904a(21) =126983569a(22) =291698040a(23) =669004352a(24) =1532095329a(25) =3503889147a(26) =8003207912a(27) =18258464741a(28) =41608726254a(29) =94722900936