A145558 Denominators of partial sums of a certain alternating series of inverse central binomial coefficients.

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.

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

Cf. A145375/A145556, A145557.

Sequence in context: A199095 A235230 A024081 * A145612 A307812 A354682

Adjacent sequences: A145555 A145556 A145557 * A145559 A145560 A145561

Keyword

nonn,frac,easy

Author

Wolfdieter Lang, Oct 17 2008

Status

approved