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Sums of powers of integers via differentiation

Number Theory 2023-03-24 v3

Abstract

For integer k0k \geq 0, let SkS_k denote the sum of the kkth powers of the first nn positive integers 1k+2k++nk1^k + 2^k + \cdots + n^k. For any given kk, the power sum SkS_k can in principle be determined by differentiating kk times (with respect to xx) the associated exponential generating function k=0Skxk/k!\sum_{k=0}^{\infty}S_k x^k/k!, and then taking the limit of the resulting differentiated function as xx approaches 00. In this paper, we exploit this method to establish a couple of seemingly novel recurrence relations, one of them involving the even-indexed power sums S2,S4,,S2kS_2, S_4,\ldots, S_{2k}, and the other the odd-indexed power sums S1,S3,,S2k1S_{1}, S_3, \ldots, S_{2k-1}, with both recurrence relations depending explicitly on the parameter N=n+12N = n + \frac{1}{2}. From this, we obtain a determinantal formula of order kk which yields S2kS_{2k} [S2k1S_{2k-1}] in the Faulhaber form, that is, as an odd [even] polynomial in NN. As a byproduct, we discover a new determinantal formula for the Bernoulli number B2kB_{2k}. Furthermore, we show that S2kS_{2k} and S2k1S_{2k-1} can be obtained by taking the corresponding higher order derivatives of the Chebyshev polynomials of the second kind.

Keywords

Cite

@article{arxiv.2303.04122,
  title  = {Sums of powers of integers via differentiation},
  author = {José L. Cereceda},
  journal= {arXiv preprint arXiv:2303.04122},
  year   = {2023}
}

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21 pages