Coefficient of x^n in the expansion of ( (1+x+x^3)^2 / (1+x) )^n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =25a(5) =61a(6) =187a(7) =666a(8) =2137a(9) =6676a(10) =22001a(11) =73217a(12) =239923a(13) =789517a(14) =2624182a(15) =8729527a(16) =29026553a(17) =96790606a(18) =323546416a(19) =1082566763a(20) =3626148425a(21) =12163438539a(22) =40847087821a(23) =137294721676a(24) =461890741843