OFFSET
2,1
COMMENTS
(2n-1)! = A009445(n-1) is the number of monomials in determinant of symbolic square matrix of size 2n-1 X 2n-1 without zeros.
Denominators in the series expansion of (1/2)*(Pi/(2*x))^(1/2)* (x*BesselI(1/2, x) - BesselI(3/2, x)). - Abdallah Daddi-Moussa-Ider, Jul 25 2024
FORMULA
a(n) = (2*n - 1)!/(2*(n - 1)^2).
Sum_{n=2..oo} 1/a(n) = (1 - 3*e^2 + 8*e*sinh(1))/(4*e) = 0.40366087623617955676434290... . - Stefano Spezia, Jul 25 2024
MATHEMATICA
Table[(2 n - 1)!/(2 (n - 1)^2), {n, 2, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski, Apr 02 2008
EXTENSIONS
a(15)-a(17) from Stefano Spezia, Jul 25 2024
STATUS
approved