a(n) = Sum_{k=0..floor(n/3)} binomial(4*n-2*k,n-3*k).
A371755
a(n) = Sum_{k=0..floor(n/3)} binomial(4*n-2*k,n-3*k).
Terms
- a(0) =1a(1) =4a(2) =28a(3) =221a(4) =1834a(5) =15657a(6) =136137a(7) =1199014a(8) =10661184a(9) =95493145a(10) =860339723a(11) =7788028028a(12) =70777321331a(13) =645359630071
External references
- oeis: A371755