a(n) = T(n, n+4), T given by A027052.

Terms

a(0) =1a(1) =18a(2) =59a(3) =146a(4) =319a(5) =652a(6) =1281a(7) =2456a(8) =4637a(9) =8670a(10) =16111a(11) =29822a(12) =55067a(13) =101528a(14) =187013a(15) =344276a(16) =633561a(17) =1165674a(18) =2144419a(19) =3944650a(20) =7255831a(21) =13346084a(22) =24547849a(23) =45151152a(24) =83046581a(25) =152747190a(26) =280946647a(27) =516742262a(28) =950438067