a(n) = Sum_{d|n} Sum{t|d} moebius(d/t)*binomial(3*t,t)/(3*d^2).

A244035

a(n) = Sum_{d|n} Sum{t|d} moebius(d/t)*binomial(3*t,t)/(3*d^2).

Terms

    a(0) =1a(1) =2a(2) =4a(3) =12a(4) =41a(5) =176a(6) =792a(7) =3840a(8) =19291a(9) =100182a(10) =533160a(11) =2897544a(12) =16020564a(13) =89898944a(14) =510914744a(15) =2936004072a(16) =17036988567a(17) =99718480238a(18) =588166176660

External references