Coefficient of x in the reduction by x^2->x+1 of the polynomial p(n,x)=1+x^n+x^(2n+2).

Terms

a(0) =4a(1) =9a(2) =23a(3) =58a(4) =149a(5) =385a(6) =1000a(7) =2605a(8) =6799a(9) =17766a(10) =46457a(11) =121537a(12) =318044a(13) =832417a(14) =2178919a(15) =5703874a(16) =14931949a(17) =39090753a(18) =102338336a(19) =267921061a(20) =701419679a(21) =1836329614a(22) =4807555633a(23) =12586315393a(24) =32951355124a(25) =86267692665a(26) =225851630135