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

A390830

a(n) = Sum_{k=0..floor(n/4)} 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) =93a(5) =351a(6) =1377a(7) =5427a(8) =21357a(9) =84159a(10) =333153a(11) =1326051a(12) =5303421a(13) =21289311a(14) =85705857a(15) =345845619a(16) =1398456333a(17) =5665268223a(18) =22988910753a(19) =93426350211a(20) =380195618589

External references