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

A391986

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

Terms

    a(0) =1a(1) =3a(2) =9a(3) =27a(4) =117a(5) =567a(6) =2673a(7) =11907a(8) =51597a(9) =222831a(10) =968841a(11) =4236219a(12) =18551781a(13) =81154791a(14) =354374433a(15) =1545091443a(16) =6729252957a(17) =29281369023a(18) =127304349273a(19) =552981937419

External references