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A122215 Denominators in infinite products for Pi/2, e and e^gamma (reduced). 5
1, 1, 3, 27, 3645, 61509375, 4204742431640625, 2396825584582984447479248046875, 3896237517467890187050354408614984136338676989907980896532535552978515625 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For n>=2 the n-th term of this sequence of rational numbers equals exp(-2 * integral(x=0..1, x^(2*n-1)/log(1-x^2) ) ) (see Mathematica code below). - John M. Campbell, Jul 18 2011

REFERENCES

Mohammad K. Azarian, Euler's Number Via Difference Equations, International Journal of Contemporary Mathematical Sciences, Vol. 7, 2012, No. 22, pp. 1095 - 1102.

J. Sondow, A faster product for Pi and a new integral for ln Pi/2, Amer. Math. Monthly 112 (2005) 729-734.

LINKS

Table of n, a(n) for n=1..9.

J. Baez, This Week's Finds in Mathematical Physics

J. Guillera and J. Sondow, Double integrals and infinite products for some classical constants via analytic continuations of Lerch's transcendent, Ramanujan J. 16 (2008) 247-270.

J. Sondow, A faster product for Pi and a new integral for ln Pi/2, arXiv:math/0401406 [math.NT], 2004.

FORMULA

a(n) = denominator(product(k=1..n, k^((-1)^k*binomial(n-1,k-1)))).

EXAMPLE

Pi/2 = (2/1)^(1/2) * (4/3)^(1/4) * (32/27)^(1/8) *

(4096/3645)^(1/16) * ...,

e = (2/1)^(1/1) * (4/3)^(1/2) * (32/27)^(1/3) * (4096/3645)^(1/4) * ... and

e^gamma = (2/1)^(1/2) * (4/3)^(1/3) * (32/27)^(1/4) * (4096/3645)^(1/5) *

...

MATHEMATICA

Table[Exp[-2*Integrate[x^(2n-1)/Log[1-x^2], {x, 0, 1}]], {n, 2, 8}]

Denominator@Table[Product[k^((-1)^k Binomial[n-1, k-1]), {k, 1, n}], {n, 1, 10}] (* Vladimir Reshetnikov, May 29 2016 *)

CROSSREFS

Cf. A092799. Numerators are A122214. Unreduced denominators are A122217.

Sequence in context: A009039 A137092 A170921 * A122217 A316368 A068221

Adjacent sequences:  A122212 A122213 A122214 * A122216 A122217 A122218

KEYWORD

frac,nonn

AUTHOR

Jonathan Sondow, Aug 26 2006

STATUS

approved

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Last modified October 23 05:45 EDT 2018. Contains 316519 sequences. (Running on oeis4.)