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A195506 Denominators of Sum_{k=1..n} H(k)/k^2; H(k) the k-th harmonic number. 2
1, 8, 216, 1728, 216000, 216000, 74088000, 592704000, 16003008000, 16003008000, 21300003648000, 21300003648000, 46796108014656000, 46796108014656000, 46796108014656000, 374368864117248000, 1839274229408039424000, 1839274229408039424000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For the numerators see A195505.

lim n--> infinity (A195505(n)/A195506(n)) = 2*Zeta(3) [L. Euler].

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..768

L. Euler, Meditationes circa singulare serierum genus, Novi. Comm. Acad. Sci. Petropolitanae, 20 (1775), 140-186.

EXAMPLE

a(2)=8 because 1 + (1+1/2)/2^2 = 11/8.

MATHEMATICA

s = 0; Table[s = s + HarmonicNumber[n]/n^2; Denominator[s], {n, 20}] (* T. D. Noe, Sep 20 2011 *)

CROSSREFS

Cf. A195505, A002117.

Sequence in context: A163289 A060459 A007409 * A069045 A288323 A264056

Adjacent sequences:  A195503 A195504 A195505 * A195507 A195508 A195509

KEYWORD

nonn,frac,easy

AUTHOR

Franz Vrabec, Sep 19 2011

STATUS

approved

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Last modified January 17 09:32 EST 2020. Contains 330949 sequences. (Running on oeis4.)