a(n) = 2*binomial(7*n-1,2*n)/(7*n-1).

A322631

a(n) = 2*binomial(7*n-1,2*n)/(7*n-1).

Terms

    a(0) =5a(1) =110a(2) =3876a(3) =164450a(4) =7713420a(5) =385300240a(6) =20096692635

External references