a(n) = (3*0^n + 4^n*binomial(2*n,n))/4.

A099045

a(n) = (3*0^n + 4^n*binomial(2*n,n))/4.

Terms

    a(0) =1a(1) =2a(2) =24a(3) =320a(4) =4480a(5) =64512a(6) =946176a(7) =14057472a(8) =210862080a(9) =3186360320a(10) =48432676864a(11) =739699064832

External references