G.f. = ((2+3*x)/(1-x^2-x^3))^2.

Terms

a(0) =4a(1) =12a(2) =17a(3) =32a(4) =54a(5) =78a(6) =127a(7) =186a(8) =275a(9) =408a(10) =585a(11) =848a(12) =1212a(13) =1722a(14) =2444a(15) =3442a(16) =4839a(17) =6778a(18) =9462a(19) =13182a(20) =18313a(21) =25390a(22) =35133a(23) =48522a(24) =66907a(25) =92112a(26) =126632a(27) =173860a(28) =238404a(29) =326536