Coefficient of x^n in 1/(n+1) * (1 + x - 3*x^2)^(n+1).

Terms

a(0) =1a(1) =1a(2) =-2a(3) =-8a(4) =1a(5) =61a(6) =91a(7) =-377a(8) =-1469a(9) =1027a(10) =16120a(11) =18250a(12) =-132065a(13) =-427517a(14) =620062a(15) =5707648a(16) =3746683a(17) =-55581941a(18) =-144227438a(19) =351490672a(20) =2274331579a(21) =278638399a(22) =-25348074713a(23) =-50842003745a(24) =195685236757a(25) =957135268261a(26) =-459626168864