a(n) = (2n-1)!! * Sum_{k=0..n-2}(-1)^k/(2k+1).
A135457
a(n) = (2n-1)!! * Sum_{k=0..n-2}(-1)^k/(2k+1).
Terms
- a(0) =0a(1) =3a(2) =10a(3) =91a(4) =684a(5) =8679a(6) =100542a(7) =1664055a(8) =25991640a(9) =532354635a(10) =10455799410a(11) =255542155155
External references
- oeis: A135457