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A006953
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a(n) = denominator of Bernoulli(2n)/(2n).
(Formerly M2039)
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19
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12, 120, 252, 240, 132, 32760, 12, 8160, 14364, 6600, 276, 65520, 12, 3480, 85932, 16320, 12, 69090840, 12, 541200, 75852, 2760, 564, 2227680, 132, 6360, 43092, 6960, 708, 3407203800, 12, 32640, 388332, 120, 9372, 10087262640
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OFFSET
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1,1
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COMMENTS
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a(n) are alternately divisible by 12 and 120, a(n)/(12, 120, 12, 120, 12, 120, ...) = 1, 1, 21, 2, 11, 273, ... . - Paul Curtz, Sep 13 2011 and Michel Marcus, Jan 05 2013
A141590/(2 before a(n+1)) = 1/2 + 1/12 - 1/120 + 1/252 is an old semi-convergent series for Euler's constants A001620 ("2 before a" meaning that one term, namely 2, is inserted before the sequence). This series is discussed in details in reference [Blagouchine, 2016], Sect. 3 and Fig. 3. - Paul Curtz, Sep 13 2011, Michel Marcus, Jan 05 2013 and Iaroslav V. Blagouchine, Sep 16 2015
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REFERENCES
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M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 259, (6.3.18) and (6.3.19); also p. 810.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math.Series 55, Tenth Printing, 1972, p. 259, (6.3.18) and (6.3.19).
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FORMULA
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Zeta(1-2*n) = -Bernoulli(2*n)/(2*n).
G.f. for Bernoulli(2*n)/(2*n) = A001067(n)/A006953(n): (-1)^n/((2*Pi)^(2*n)*(2*n)) * Integral_{t=0..1} log(1-1/t)^(2*n) dt. - Gerry Martens, May 18 2011
E.g.f.: a(n) = denominator((2*n+1)!*[x^(2*n+1)](1/(1-1/exp(x)))). - Peter Luschny, Jul 12 2012
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EXAMPLE
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Sequence Bernoulli(2n)/(2n) (n >= 1) begins 1/12, -1/120, 1/252, -1/240, 1/132, -691/32760, 1/12, -3617/8160, ... .
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MAPLE
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A006953_list := proc(n) 1/(1-1/exp(z)); series(%, z, 2*n+4);
seq(denom((-1)^i*(2*i+1)!*coeff(%, z, 2*i+1)), i=0..n) end;
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MATHEMATICA
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Table[Denominator[BernoulliB[2n]/(2n)], {n, 40}] (* Harvey P. Dale, Jan 12 2022 *)
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PROG
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(Magma) [Denominator(Bernoulli(2*n)/(2*n)):n in [1..40]]; // Vincenzo Librandi, Sep 17 2015
(PARI) a(n) = denominator(bernfrac(2*n)/(2*n)); \\ Michel Marcus, Apr 21 2016
(Sage) [denominator(bernoulli(2*n)/(2*n)) for n in (1..40)] # G. C. Greubel, Sep 19 2019
(GAP) List([1..40], n-> DenominatorRat(Bernoulli(2*n)/(2*n)) ); # G. C. Greubel, Sep 19 2019
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CROSSREFS
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KEYWORD
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nonn,frac,easy,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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