G.f.: Sum_{n=-oo..+oo} x^n * (1 + x^n)^n, an even function.

Terms

a(0) =2a(1) =4a(2) =2a(3) =10a(4) =2a(5) =12a(6) =16a(7) =16a(8) =2a(9) =50a(10) =24a(11) =24a(12) =58a(13) =28a(14) =72a(15) =154a(16) =2a(17) =36a(18) =302a(19) =40a(20) =142a(21) =270a(22) =332a(23) =48a(24) =242a(25) =472a(26) =574a(27) =614a(28) =60a(29) =60