Because all summands are machine integers Mathematica can use internal.
Publishing, pp. 423–446, MR 0827799, Zbl 0634. Let us compare the timings of various ways to sum the term of longList.
Japan 1984 (Tokyo, Okayama and Kyoto, 1984), Singapore: World Sci. (1985), "On congruences arising from relative Gauss sums", Number theory and combinatorics.
#Summation in mathematica how to
system like GiNaC 38, FORM 39 or the commercial ones like Mathematica or Maple. Keywords: Lattice sum Helmholtz equation Ewald summation lattice reduction Clausen function Schlmilch series. (1979), "Sums of Gauss, Eisenstein, Jacobi, Jacobsthal, and Brewer", Illinois Journal of Mathematics, 23 (3): 374–437, ISSN 0019-2082, MR 0537798, Zbl 0393.12029 algebraic structure of nested sums forms a Hopf algebra 36, 37.