a(n) = 2^n*binomial(5*n, n)/(4*n+1).

A217364

a(n) = 2^n*binomial(5*n, n)/(4*n+1).

Terms

    a(0) =1a(1) =2a(2) =20a(3) =280a(4) =4560a(5) =80960a(6) =1520064a(7) =29680640a(8) =596593920a(9) =12262581760a(10) =256556410880

External references