a(n) = A027113(n, 2n-7).

Terms

a(0) =1a(1) =4a(2) =13a(3) =44a(4) =149a(5) =500a(6) =1660a(7) =5444a(8) =17640a(9) =56524a(10) =179322a(11) =563932a(12) =1759982a(13) =5456608a(14) =16821309a(15) =51600720a(16) =157615653a(17) =479664388a(18) =1455061181a(19) =4401607356a(20) =13282579293a(21) =39997017088a(22) =120215762283a(23) =360730451088