Sum of generalized alternating harmonic series with three periodically repeated numerators

This contribution deals with the generalized convergent harmonic series with three periodically repeated numerators; i. e. with periodically repeated numerators , where . Firstly, it is derived that the only value of the coefficient , for which this series converges, is . Then the formula for the sum of this series is analytically derived. A relation for calculation the value of the constant from an arbitrary sum also follows from the derived formula. The obtained analytical results are finally numerically verified by using the computer algebra system Maple 15 and its basic programming language.


INTRODUCTION
Let us recall the basic terms and notions.The harmonic series is the sum of reciprocals of all natural numbers except zero (see e.g.web page [4]), so this is the series The divergence of this series can be easily proved e.g. by using the integral test or the comparison test of convergence.The series  Corresponding author: Radovan Potůček, University of Defence, Faculty of Military, Technology Department of Mathematics and Physics, Kounicova 65, 662 10 Brno, Czech Republic.E-mail: Radovan.Potucek@unob.cz is known as the alternating harmonic series.This series converges by the alternating series test.In particular, the sum (interesting information about sum of series can be found e.g. in book [2] or paper [1]) is equal to the natural logarithm of 2: This formula is a special case of the Mercator series, the Taylor series for the natural logarithm: The series converges to the natural logarithm (shifted by 1) whenever .

Sum of generalized alternating harmonic series with three periodically repeated numerators
We deal with the numerical series of the form where are appropriate constants for which the series (1) converges.This series we shall call generalized convergent harmonic series with periodically repeated numerators .We determine the values of the numerators , for which the series (1) converges, and the sum of this series.The power series corresponding to the series (1) has evidently the form
Very small difference both and accuracy of the sum are caused by the fact that the triplet is a fraction with small constant numerator independent of the variable .
Table 1 The approximate values of the sums of the generalized harmonic series with three periodically repeating numerators for some non-negative integers Table 2 The approximate values of the sums of the generalized harmonic series with three periodically repeating numerators for some negative integers Table 3 The approximate values of the sums of the generalized harmonic series with three periodically repeating numerators for some in the fractional form Computation of 126 values , above took about 74 800 seconds, i.e. almost 20 hours 47 minutes.The relative quantification accuracies of the sums are, except the value , approximately between and .

CONCLUSIONS
In this paper we dealt with the generalized convergent harmonic series with three periodically repeated numerators , where , i.e. with the series We derived that the only value of the coefficient , for which this series converges, is , and we also derived that the sum of this series is determined by the formula .18 This formula allows determine other sums whose three periodically repeated numerators need not be , but also for arbitrary , at least one nonzero.For example, the series has the sum .Finally, we verified the main result by computing some sums by using the CAS Maple 15 and its basic programming language.These generalized alternating harmonic series so belong to special types of convergent infinite series, such as geometric and telescoping series, which sum can be found analytically and also presented by means of a simple numerical expression.From the derived formula above it follows that This relation allows calculate the value of the constant for a given sum , as illustrates the following table: We denote its sum by .The series (2) is for absolutely convergent, so we can rearrange it and rewrite it in the form If we differentiate the series (3) term-by-term, where , we get After reindexing and fine arrangement the series (4) for we obtain that is When we summate the convergent geometric series (11) which has the first term and the ratio , where , i.e. for , we get We convert this fraction using the CAS Maple 15 to partial fractions and get where .The sum of the series (2) we obtain by integration in the form From the condition we obtain hence Now, we will deal with the convergence of the series (2) in the right point .After substitution to the power series (2) -it can be done by the extended version of Abel's theorem (see [5], p. 23)we get the numerical series (1).By the integral test we can prove that the series (1) converges if and only if .After simplification the equation (6), where , we have For , because and after re-mark as , we get a simple formula sumgenhar1ab:=proc(t,a) local r,k,s; s:=0; r:=0; for k from 1 to t do r:=1/(3*k-2) + a/(3*k-1) -(a+1)/(3*k); s:=s+r; end do; print("t=",k-1,"s(",a,")=",evalf[20](s)); end proc:

Table 4
The approximate values of the constant for some sums of the generalized harmonic series with three periodically repeating numerators , where Mathematics in Education, Research and Applications (MERAA), ISSN 2453-6881 Math Educ Res Appl, 2015(1), 1