a(n) = T(3n,n), where T = Delannoy triangle (A008288).

A026001

a(n) = T(3n,n), where T = Delannoy triangle (A008288).

Terms

    a(0) =1a(1) =7a(2) =85a(3) =1159a(4) =16641a(5) =246047a(6) =3707509a(7) =56610575a(8) =872893441a(9) =13560999991a(10) =211939849045

External references