G.f.: Sum_{n>=0} x^n * (1 + x^n)^n / (1 + x + x^(n+1))^(n+1).

Terms

a(0) =1a(1) =-1a(2) =4a(3) =-11a(4) =24a(5) =-47a(6) =95a(7) =-204a(8) =440a(9) =-915a(10) =1829a(11) =-3556a(12) =6819a(13) =-13043a(14) =25039a(15) =-48306a(16) =93509a(17) =-181219a(18) =351089a(19) =-679814a(20) =1316526a(21) =-2552828a(22) =4961602a(23) =-9672267a(24) =18916895a(25) =-37114623a(26) =73027149a(27) =-144047576a(28) =284741852a(29) =-563872928