a(n) = Sum_{k=0..n} 2^k*(n!/k!)^2.
A228513
a(n) = Sum_{k=0..n} 2^k*(n!/k!)^2.
Terms
- a(0) =1a(1) =3a(2) =16a(3) =152a(4) =2448a(5) =61232a(6) =2204416a(7) =108016512a(8) =6913057024a(9) =559957619456
External references
- oeis: A228513
A228513
a(n) = Sum_{k=0..n} 2^k*(n!/k!)^2.