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A145558
Denominators of partial sums of a certain alternating series of inverse central binomial coefficients.
5
1, 6, 15, 420, 36, 1386, 36036, 40040, 6126120, 2116296, 255816, 267711444, 3346393050, 1745944200, 6850263420, 14440355289360, 1604483921040, 3800093497200, 2671465728531600, 534293145706320, 952435607563440, 941958815880242160, 362291852261631600
OFFSET
1,2
COMMENTS
See A145557 for the numerators, references and a W. Lang link.
FORMULA
a(n)=(1/2)*denominator(r(n)), with the rationals (in lowest terms) r(n):=sum(((-1)^(k+1))/(k*binomial(2*k,k)),k=1..n).
EXAMPLE
Rationals r(n) (in lowest terms): [1/2, 5/12, 13/30, 361/840, 31/72, 1193/2772, 31021/72072,...].
CROSSREFS
KEYWORD
nonn,frac,easy
AUTHOR
Wolfdieter Lang, Oct 17 2008
STATUS
approved