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

A392032

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

Terms

    a(0) =1a(1) =1a(2) =7a(3) =19a(4) =73a(5) =241a(6) =831a(7) =2787a(8) =9339a(9) =31003a(10) =102373a(11) =336073a(12) =1097911a(13) =3570607a(14) =11565529a(15) =37324437a(16) =120052107a(17) =384962859a(18) =1230978093a(19) =3926097681a(20) =12492150819a(21) =39660238779a(22) =125656218933a(23) =397360559841

External references