a(n) = sum of absolute values of coefficients of (1 + x - 2*x^2)^n.

Terms

a(0) =1a(1) =4a(2) =14a(3) =44a(4) =124a(5) =394a(6) =1418a(7) =4706a(8) =14322a(9) =40712a(10) =135878a(11) =468934a(12) =1513650a(13) =4502864a(14) =13421408a(15) =45258442a(16) =152708520a(17) =483810550a(18) =1413811358a(19) =4483843328a(20) =15051967962a(21) =49724234652a(22) =154802614364a(23) =461020649750