a(n) = (1/n)*Sum_{i=0..n-1} C(n,i)*C(n,i+1)*4^i*5^(n-i), a(0) = 1.
A133305
a(n) = (1/n)*Sum_{i=0..n-1} C(n,i)*C(n,i+1)*4^i*5^(n-i), a(0) = 1.
Terms
- a(0) =1a(1) =5a(2) =45a(3) =505a(4) =6345a(5) =85405a(6) =1204245a(7) =17558705a(8) =262577745a(9) =4005148405a(10) =62070886845a(11) =974612606505
External references
- oeis: A133305