a(n) = Sum_{k=0..floor(n/3)} binomial(3*n-3*k+1,n-3*k).
A390703
a(n) = Sum_{k=0..floor(n/3)} binomial(3*n-3*k+1,n-3*k).
Terms
- a(0) =1a(1) =4a(2) =21a(3) =121a(4) =725a(5) =4446a(6) =27693a(7) =174436a(8) =1108080a(9) =7085541a(10) =45548877a(11) =294085065a(12) =1905673810a(13) =12386964125a(14) =80729648541a(15) =527353208457
External references
- oeis: A390703