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

A392033

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

Terms

    a(0) =1a(1) =1a(2) =9a(3) =25a(4) =109a(5) =381a(6) =1421a(7) =5069a(8) =18075a(9) =63499a(10) =221323a(11) =764523a(12) =2621587a(13) =8928115a(14) =30220347a(15) =101721707a(16) =340659227a(17) =1135543323a(18) =3769023795a(19) =12460643043a(20) =41045661279a(21) =134748546639a(22) =440974812831

External references