a(n) = A027082(n, 2n-4).

Terms

a(0) =1a(1) =1a(2) =5a(3) =17a(4) =54a(5) =169a(6) =517a(7) =1559a(8) =4653a(9) =13787a(10) =40638a(11) =119333a(12) =349469a(13) =1021433a(14) =2981330a(15) =8693467a(16) =25333627a(17) =73795263a(18) =214915073a(19) =625855927a(20) =1822630172a(21) =5308552227a(22) =15464475465a(23) =45060652609a(24) =131334677147a(25) =382907083385