a(n) = (1/(2*n+1)) * Sum_{k=0..n} (k+1)^3 * (2*k+1) * binomial(3*n-k,n-k).
A390969
a(n) = (1/(2*n+1)) * Sum_{k=0..n} (k+1)^3 * (2*k+1) * binomial(3*n-k,n-k).
Terms
- a(0) =1a(1) =9a(2) =54a(3) =307a(4) =1743a(5) =9996a(6) =58026a(7) =340791a(8) =2022735a(9) =12118665a(10) =73207368a(11) =445468884a(12) =2728222084a(13) =16804731336a(14) =104041748994a(15) =647113502847
External references
- oeis: A390969