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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

See A145557 for the numerators, references and a W. Lang link.

LINKS

Table of n, a(n) for n=1..23.

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

A145375/A145556.

Sequence in context: A199095 A235230 A024081 * A145612 A307812 A280964

Adjacent sequences:  A145555 A145556 A145557 * A145559 A145560 A145561

KEYWORD

nonn,easy

AUTHOR

Wolfdieter Lang Oct 17 2008

STATUS

approved

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Last modified November 13 00:25 EST 2019. Contains 329083 sequences. (Running on oeis4.)