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

A387512

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

Terms

    a(0) =1a(1) =3a(2) =9a(3) =33a(4) =153a(5) =729a(6) =3357a(7) =15309a(8) =70713a(9) =331425a(10) =1565325a(11) =7418061a(12) =35250633a(13) =168030369a(14) =803361645a(15) =3850647741a(16) =18495465561a(17) =88998869313a(18) =428955792525

External references