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A145567
Denominators of partial sums of a certain series of inverse central binomial coefficients.
1
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.
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
KEYWORD
nonn,frac,easy
AUTHOR
Wolfdieter Lang, Oct 17 2008, Oct 28 2008
STATUS
approved