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

Terms

a(0) =1a(1) =2a(2) =4a(3) =16a(4) =56a(5) =200a(6) =712a(7) =2536a(8) =9032a(9) =32168a(10) =114568a(11) =408040a(12) =1453256a(13) =5175848a(14) =18434056a(15) =65653864a(16) =233829704a(17) =832796840a(18) =2966049928a(19) =10563743464a(20) =37623330248a(21) =133997477672a(22) =477239093512