OFFSET
0,2
COMMENTS
Equivalently, denominators in partial products of the following approximation to Pi: Pi = Product_{n>=1} 4*n^2/(4*n^2-1). Numerators are in A056982.
REFERENCES
O. J. Farrell and B. Ross, Solved Problems in Analysis, Dover, NY, 1971; p. 77.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..832
B. Gourevitch, L'univers de Pi
FORMULA
a(n) = numerator(W(n)), where W(n) = (2*n)!*(2*n+1)!/((2^n)*n!)^4.
a(n) = (-1)^n*A056982(n)*C(-1/2,n)*C(n+1/2,n). - Peter Luschny, Apr 08 2016
PROG
(PARI) a(n) = numerator(prod(k=1, n, 1-1/(4*k^2))); \\ Michel Marcus, Oct 22 2016
CROSSREFS
KEYWORD
nonn,frac,easy
AUTHOR
Benoit Cloitre, Apr 27 2002
STATUS
approved