Next-to-middle coefficient in expansion of Product_{k=1..n} (1 + x^k).

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =3a(5) =5a(6) =8a(7) =13a(8) =23a(9) =39a(10) =69a(11) =123a(12) =219a(13) =396a(14) =719a(15) =1313a(16) =2406a(17) =4435a(18) =8215a(19) =15260a(20) =28431a(21) =53167a(22) =99774a(23) =187615a(24) =353500a(25) =667874a(26) =1264854a(27) =2399207a(28) =4557831a(29) =8675836