a(n) = (1/(2*n+1)) * Sum_{k=0..n} (k+1)^2 * (2*k+1) * binomial(3*n-k,n-k).
A390968
a(n) = (1/(2*n+1)) * Sum_{k=0..n} (k+1)^2 * (2*k+1) * binomial(3*n-k,n-k).
Terms
- a(0) =1a(1) =5a(2) =24a(3) =121a(4) =637a(5) =3468a(6) =19380a(7) =110561a(8) =641355a(9) =3771885a(10) =22439040a(11) =134796060a(12) =816540124a(13) =4982228488a(14) =30593078076a(15) =188908910769
External references
- oeis: A390968