a(n) = Sum_{k=0..n} (-1)^k * binomial(3*n+3*k+1,n-k).
A390545
a(n) = Sum_{k=0..n} (-1)^k * binomial(3*n+3*k+1,n-k).
Terms
- a(0) =1a(1) =3a(2) =12a(3) =57a(4) =305a(5) =1759a(6) =10604a(7) =65616a(8) =412583a(9) =2621660a(10) =16782273a(11) =108025849a(12) =698383407a(13) =4531073261a(14) =29484836431a(15) =192352647208
External references
- oeis: A390545