a(n) = Sum_{k=0..n} C(k*(k+1)/2, k) * C(k*(k+1)/2, n-k).
A137646
a(n) = Sum_{k=0..n} C(k*(k+1)/2, k) * C(k*(k+1)/2, n-k).
Terms
- a(0) =1a(1) =1a(2) =4a(3) =29a(4) =339a(5) =5406a(6) =109159a(7) =2664399a(8) =76219485a(9) =2499425650a(10) =92402751894
External references
- oeis: A137646