a(n) = sum of the absolute values of the coefficients in (1+x-x^3)^n.

Terms

a(0) =1a(1) =3a(2) =9a(3) =25a(4) =63a(5) =171a(6) =471a(7) =1193a(8) =3209a(9) =8841a(10) =22537a(11) =60393a(12) =165489a(13) =424451a(14) =1134849a(15) =3093893a(16) =7987289a(17) =21288933a(18) =57973543a(19) =150409931a(20) =399788279a(21) =1085870421a(22) =2831439537a(23) =7501994181a(24) =20330726077a(25) =53274740933a(26) =140615421393a(27) =380366331549