a(n) = (2*n + 4) * (1*3*5*...*(2*n+1))^2.

A003955

a(n) = (2*n + 4) * (1*3*5*...*(2*n+1))^2.

Terms

    a(0) =4a(1) =54a(2) =1800a(3) =110250a(4) =10716300a(5) =1512784350a(6) =292183491600

External references