English

Summation of rational series twisted by strongly B-multiplicative coefficients

Number Theory 2015-05-19 v4

Abstract

We evaluate in closed form series of the type u(n)R(n)\sum u(n) R(n), where (u(n))n(u(n))_n is a strongly BB-multiplicative sequence and R(n)R(n) a (well-chosen) rational function. A typical example is: n1(1)s2(n)4n+12n(2n+1)(2n+2)=14 \sum_{n \geq 1} (-1)^{s_2(n)} \frac{4n+1}{2n(2n+1)(2n+2)} = -\frac{1}{4} where s2(n)s_2(n) is the sum of the binary digits of the integer nn. Furthermore closed formulas for series involving automatic sequences that are not strongly BB-multiplicative, such as the regular paperfolding and Golay-Shapiro-Rudin sequences, are obtained; for example, for integer d0d \geq 0: n0v(n)(n+1)2d+1=π2d+1E2d(22d+22)(2d)! \sum_{n \geq 0} \frac{v(n)}{(n+1)^{2d+1}} = \frac{\pi^{2d+1} |E_{2d}|}{(2^{2d+2}-2)(2d)!} where (v(n))n(v(n))_n is the ±1\pm 1 regular paperfolding sequence and E2dE_{2d} is an Euler number.

Keywords

Cite

@article{arxiv.1408.5770,
  title  = {Summation of rational series twisted by strongly B-multiplicative coefficients},
  author = {Jean-Paul Allouche and Jonathan Sondow},
  journal= {arXiv preprint arXiv:1408.5770},
  year   = {2015}
}

Comments

Typo in a crossreference corrected in Example 9, page 6. Remark added top of Page 9 about the relation between paperfolding and the Jacobi-Kronecker symbol