A145567 Denominators of partial sums of a certain series of inverse central binomial coefficients.

1, 20, 28, 168, 9240, 10010, 30030, 4084080, 2351440, 2351440, 594914320, 1487285800, 2677114440, 22181805360, 67415290800, 404491744800, 48134517631200, 197886350261600, 593659050784800, 24340021082176800, 15168418935269600, 136515770417426400

Offset

2,2

Comments

See A145566 for the numerators, a reference and a W. Lang link.

Links

Table of n, a(n) for n=2..23.

Formula

a(n) = denominator(r(n))/6, with the rationals (in lowest terms) r(n) := Sum_{k=2..n} 1/(binomial(2*k,k)*(k-1)), n >= 2.

Example

Rationals 6*r(n) (in lowest terms): [1, 23/20, 33/28, 199/168, 10957/9240, 11873/10010, 35621/30030, 4844519/4084080, ...].

Crossrefs

Cf. A145566.

Sequence in context: A139703 A317924 A355445 * A344795 A043109 A045207

Adjacent sequences: A145564 A145565 A145566 * A145568 A145569 A145570

Keyword

nonn,frac,easy

Author

Wolfdieter Lang, Oct 17 2008, Oct 28 2008

Status

approved