a(n) = T(n, 2*n-6), T given by A027960.

Terms

a(0) =1a(1) =4a(2) =11a(3) =29a(4) =73a(5) =171a(6) =370a(7) =743a(8) =1397a(9) =2482a(10) =4201a(11) =6821a(12) =10685a(13) =16225a(14) =23976a(15) =34591a(16) =48857a(17) =67712a(18) =92263a(19) =123805a(20) =163841a(21) =214103a(22) =276574a(23) =353511a(24) =447469a(25) =561326a(26) =698309a(27) =862021a(28) =1056469a(29) =1286093