a(n) = binomial(4*n, 2*n) - 4*n*binomial(2*n-2, n-1).

A305693

a(n) = binomial(4*n, 2*n) - 4*n*binomial(2*n-2, n-1).

Terms

    a(0) =1a(1) =2a(2) =54a(3) =852a(4) =12550a(5) =183356a(6) =2698108a(7) =40090728a(8) =600970566a(9) =9074671980a(10) =137844584020

External references