a(n) = (1/(2*n+1)) * Sum_{k=0..n} k^2 * (2*k+1) * binomial(3*n-k,n-k).
A390971
a(n) = (1/(2*n+1)) * Sum_{k=0..n} k^2 * (2*k+1) * binomial(3*n-k,n-k).
Terms
- a(0) =0a(1) =1a(2) =7a(3) =41a(4) =234a(5) =1340a(6) =7752a(7) =45353a(8) =268180a(9) =1601145a(10) =9641775a(11) =58503324a(12) =357377672a(13) =2196211368a(14) =13568830772a(15) =84235073385a(16) =525193567528
External references
- oeis: A390971