A145556 Denominators of partial sums of the alternating series of inverse central binomial coefficients.

2, 3, 60, 84, 126, 2772, 72072, 360360, 1225224, 23279256, 11639628, 503217, 13385572200, 2007835830, 465817912560, 2888071057872, 627841534320, 2489716429200, 534293145706320, 18423901576080, 4381203794791824, 941958815880242160, 261655226633400600

Offset

1,1

Comments

See A145375 for the numerators, references and a W. Lang link.

Links

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

Formula

a(n) = denominator(r(n)), with the rationals (in lowest terms) r(n) := Sum_{k=1..n} (-1)^(k+1)/binomial(2*k,k).

Example

Rationals r(n) (in lowest terms): [1/2, 1/3, 23/60, 31/84, 47/126, 1031/2772, 26827/72072, ...].

Crossrefs

Cf. A145375, A145557/A145558.

Sequence in context: A299172 A154253 A097961 * A124083 A112098 A144545

Adjacent sequences: A145553 A145554 A145555 * A145557 A145558 A145559

Keyword

nonn,frac,easy

Author

Wolfdieter Lang, Oct 17 2008, Nov 17 2008, Nov 25 2008

Status

approved