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A129661 Denominators of the Engel partial sums for L(3, chi3), where L(s, chi3) is the Dirichlet L-function for the non-principal character modulo 3. 15
1, 2, 4, 8, 112, 10528, 3916416, 453977888, 5984725643520, 24757413551258752, 36544913291284069002240, 3209228105587401803500707840, 206085396642453387914503205007360 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

Leonhard Euler, "Introductio in Analysin Infinitorum", First Part, Articles 176 and 292

LINKS

Table of n, a(n) for n=0..12.

FORMULA

chi3(k) = Kronecker(-3, k); chi3(k) is 0, 1, -1 when k reduced modulo 3 is 0, 1, 2, respectively; chi3 is A049347 shifted.

Series: L(3, chi3) = Sum_{k=1..infinity} chi3(k) k^{-3} = 1 - 1/2^3 + 1/4^3 - 1/5^3 + 1/7^3 - 1/8^3 + 1/10^3 - 1/11^3 + ...

Closed form: L(3, chi3) = 4 Pi^3/(81 sqrt(3)).

EXAMPLE

L(3, chi3) = 0.8840238117500798567430579168710118077... = 1/2 + 1/(2*2) + 1/(2*2*2) + 1/(2*2*2*14) + 1/(2*2*2*14*94) + ..., the partial sums of which are 0, 1/2, 3/4, 7/8, 99/112, 9307/10528, ...

MATHEMATICA

nmax = 100; prec = 2000 (* Adjust the precision depending on nmax. *); c = N[ 4 Pi^3/(81 Sqrt[3]), prec]; e = First@Transpose@NestList[{Ceiling[1/(#[[1]] #[[2]] - 1)], #[[1]] #[[2]] - 1}&, {Ceiling[1/c], c}, nmax - 1]; Denominator[ FoldList[Plus, 0, 1/Drop[ FoldList[Times, 1, e], 1 ] ] ]

CROSSREFS

Cf. A129404, A129405, A129406, A129407, A129408, A129409, A129410, A129411.

Cf. A129658, A129659, A129660, A129662, A129663, A129664, A129665.

Sequence in context: A018666 A018686 A018694 * A018713 A007633 A018777

Adjacent sequences:  A129658 A129659 A129660 * A129662 A129663 A129664

KEYWORD

nonn,frac,easy

AUTHOR

Stuart Clary, Apr 30 2007

STATUS

approved

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Last modified September 23 14:38 EDT 2021. Contains 347618 sequences. (Running on oeis4.)