G.f.: (x^3+6*x+2)^2/(x^2+x+1)^2.

Terms

a(0) =4a(1) =16a(2) =-8a(3) =-36a(4) =72a(5) =-36a(6) =-63a(7) =126a(8) =-63a(9) =-90a(10) =180a(11) =-90a(12) =-117a(13) =234a(14) =-117a(15) =-144a(16) =288a(17) =-144a(18) =-171a(19) =342a(20) =-171a(21) =-198a(22) =396a(23) =-198a(24) =-225a(25) =450a(26) =-225a(27) =-252a(28) =504a(29) =-252