Expansion of (1-x-x^2)/(1-3x-x^2).

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =66a(5) =218a(6) =720a(7) =2378a(8) =7854a(9) =25940a(10) =85674a(11) =282962a(12) =934560a(13) =3086642a(14) =10194486a(15) =33670100a(16) =111204786a(17) =367284458a(18) =1213058160a(19) =4006458938a(20) =13232434974a(21) =43703763860a(22) =144343726554a(23) =476734943522