a(n) = (1/(3*n))*Sum_{d|n, d even} phi(2*n/d)*binomial(3d/2,d).

A082936

a(n) = (1/(3*n))*Sum_{d|n, d even} phi(2*n/d)*binomial(3d/2,d).

Terms

    a(0) =1a(1) =1a(2) =3a(3) =10a(4) =43a(5) =201a(6) =1038a(7) =5538a(8) =30667a(9) =173593a(10) =1001603a(11) =5864750a(12) =34769374a(13) =208267320a(14) =1258579654a(15) =7663720710a(16) =46976034379a(17) =289628805623

External references