G.f.: x^4*(2 - x^2 + x^3 + x^4)/(1-x-x^2)^3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =6a(6) =17a(7) =42a(8) =97a(9) =212a(10) =446a(11) =910a(12) =1813a(13) =3542a(14) =6809a(15) =12912a(16) =24202a(17) =44910a(18) =82609a(19) =150786a(20) =273353a(21) =492532a(22) =882598a(23) =1573766a(24) =2793605a(25) =4938670a(26) =8698129a(27) =15266688a(28) =26710610a(29) =46595766