a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ... + a(n-3)*a(3) for n >= 4, with initial terms 1, 1, 3, 3.

Terms

a(0) =1a(1) =1a(2) =3a(3) =3a(4) =6a(5) =18a(6) =42a(7) =105a(8) =291a(9) =792a(10) =2181a(11) =6177a(12) =17628a(13) =50679a(14) =147255a(15) =430917a(16) =1268292a(17) =3754926a(18) =11172828a(19) =33389040a(20) =100181994a(21) =301682709a(22) =911436117a(23) =2761852011a(24) =8392005462a(25) =25563691341a(26) =78053071611a(27) =238830914937a(28) =732247187460