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

Terms

a(0) =1a(1) =1a(2) =5a(3) =19a(4) =77a(5) =326a(6) =1391a(7) =6028a(8) =26349a(9) =116011a(10) =513730a(11) =2285570a(12) =10208111a(13) =45742724a(14) =205550840a(15) =925918544a(16) =4179740909a(17) =18903381337a(18) =85635147983a(19) =388517336189