G.f.: Limit_{K->oo} Sum_{n=-oo..+oo} x^(n-K) * (1 - x^n + n*(n+1)/6 * x^(n+K))^n.

Terms

a(0) =1a(1) =0a(2) =4a(3) =0a(4) =5a(5) =0a(6) =20a(7) =-24a(8) =35a(9) =0a(10) =0a(11) =0a(12) =84a(13) =-160a(14) =200a(15) =0a(16) =-150a(17) =0a(18) =460a(19) =-560a(20) =286a(21) =0a(22) =140a(23) =-200a(24) =455a(25) =-1440a(26) =2100a(27) =0a(28) =-2180a(29) =0