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

A378464

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

Terms

    a(0) =1a(1) =1a(2) =3a(3) =13a(4) =63a(5) =306a(6) =1473a(7) =7085a(8) =34239a(9) =166459a(10) =813618a(11) =3994200a(12) =19678233a(13) =97239130a(14) =481740885a(15) =2392004853a(16) =11900655999a(17) =59312062026a(18) =296071376307

External references