G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} binomial(n,k)^2 * x^k*(4-x)^(n-k).
A217461
G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} binomial(n,k)^2 * x^k*(4-x)^(n-k).
Terms
- a(0) =1a(1) =4a(2) =16a(3) =72a(4) =350a(5) =1768a(6) =9120a(7) =47696a(8) =251974a(9) =1341560a(10) =7186912a(11) =38694000a(12) =209187884a(13) =1134838736a(14) =6174666560a(15) =33681995936a(16) =184138474182
External references
- oeis: A217461