a(n) = [x^n] ((x^2 - 1)*(x^2 + x - 1))/(x^2 + 2*x - 1)^2.

Terms

a(0) =1a(1) =3a(2) =8a(3) =23a(4) =64a(5) =175a(6) =472a(7) =1259a(8) =3328a(9) =8731a(10) =22760a(11) =59007a(12) =152256a(13) =391239a(14) =1001656a(15) =2556115a(16) =6503936a(17) =16505651a(18) =41788616a(19) =105571303a(20) =266181440a(21) =669923039a(22) =1683255448a(23) =4222878651a(24) =10579130112a(25) =26467818315a(26) =66138242984a(27) =165077936207a(28) =411584855488