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

A387617

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

Terms

    a(0) =1a(1) =0a(2) =2a(3) =15a(4) =70a(5) =325a(6) =1631a(7) =8302a(8) =42150a(9) =215160a(10) =1105577a(11) =5705128a(12) =29535883a(13) =153363665a(14) =798418070a(15) =4165950640a(16) =21779722550a(17) =114064347585a(18) =598308942080

External references