a(n) = Sum_{k=0..floor(n/4)} (k+1) * 2^k * 3^(n-3*k) * binomial(n-2*k,k) * binomial(n-3*k,k).

A391985

a(n) = Sum_{k=0..floor(n/4)} (k+1) * 2^k * 3^(n-3*k) * binomial(n-2*k,k) * binomial(n-3*k,k).

Terms

    a(0) =1a(1) =3a(2) =9a(3) =27a(4) =105a(5) =459a(6) =2025a(7) =8667a(8) =36369a(9) =151875a(10) =636417a(11) =2679075a(12) =11308761a(13) =47779227a(14) =201873465a(15) =852827211a(16) =3602606625a(17) =15218565363a(18) =64287833841a(19) =271557920115

External references