Variants of Grönwall's theorem - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-21T14:19:29Z http://mathoverflow.net/feeds/question/28235 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/28235/variants-of-gronwalls-theorem Variants of Grönwall's theorem nikmil 2010-06-15T10:29:46Z 2010-06-16T01:28:53Z <p>Except the original Grönwall's theorem that $$\limsup_{n \to \infty} \frac{\sigma(n)}{n \log \log n} = e^{\gamma},$$ and the two variants $$\limsup_{\begin{smallmatrix} n\to\infty\cr n\ \text{is square free}\end{smallmatrix}} \frac{\sigma(n)}{n \log \log n} = \frac{6e^{\gamma}}{\pi^2}$$ and $$\limsup_{\begin{smallmatrix} n\to\infty\cr n\ \text{is odd}\end{smallmatrix}} \frac{\sigma(n)}{n \log \log n} = \frac{e^{\gamma}}{2}$$ that have been proven <a href="http://www.mpim-bonn.mpg.de/preprints/send?bid=2960" rel="nofollow">here</a>, are there any other similar statements known?</p> http://mathoverflow.net/questions/28235/variants-of-gronwalls-theorem/28328#28328 Answer by Will Jagy for Variants of Grönwall's theorem Will Jagy 2010-06-16T01:00:31Z 2010-06-16T01:28:53Z <p>One example possessing a limit is the colossally abundant numbers of Alaoglu and Erdos,<br> <a href="http://en.wikipedia.org/wiki/Colossally_abundant_number" rel="nofollow">http://en.wikipedia.org/wiki/Colossally_abundant_number</a> </p> <p>where the limit of the Choie, Lichiardopol, Moree and Sole's $$f_1(a_n) = \frac{\sigma(a_n)}{a_n \log \log a_n}$$ is the same $$e^\gamma .$$ That is, the limit for these numbers is the lim sup for all numbers.</p> <p>These are more natural than people realize. There is a simple recipe that takes some $\epsilon > 0$ and gives an explicit factorization for the best value $n_\epsilon;$ see page 7 in the Briggs pdf "Notes on the Riemann hypothesis and abundant numbers" at the bottom of the Wikipedia entry. The exponent of a prime $p$ in the factorization of $n_\epsilon$ is $$\left\lfloor \log_p \left( \frac{p^{1 + \epsilon} - 1}{p^\epsilon -1} \right) \right\rfloor - 1$$</p> <p>The process of making a sequence of "champion" numbers this way was invented by Ramanujan.</p>