a(n) = [x^n] ((x - 1)*(x + 1)*(2*x^2 - 1))/(2*x^4 + 4*x^3 - x^2 - 3*x + 1).

Terms

a(0) =1a(1) =3a(2) =7a(3) =20a(4) =55a(5) =151a(6) =414a(7) =1133a(8) =3099a(9) =8472a(10) =23155a(11) =63275a(12) =172894a(13) =472393a(14) =1290663a(15) =3526256a(16) =9634071a(17) =26321031a(18) =71910814a(19) =196464677a(20) =536752579a(21) =1466437096a(22) =4006383531a(23) =10945648019a(24) =29904074046a(25) =81699461841a(26) =223207100431a(27) =609813170912