# Landau’s function for one million billions

• [1] Université de Lyon, Université de Lyon 1, CNRS, Institut Camille Jordan, Bât. Doyen Jean Braconnier, 21 Avenue Claude Bernard, F-69622 Villeurbanne cedex, France.
• [2] Centre de Recherche INRIA Nancy Grand Est Projet CACAO -bâtiment A 615 rue du Jardin Botanique, F-54602 Villers-lès-Nancy cedex, France.
• Volume: 20, Issue: 3, page 625-671
• ISSN: 1246-7405

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## Abstract

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Let ${𝔖}_{n}$ denote the symmetric group with $n$ letters, and $g\left(n\right)$ the maximal order of an element of ${𝔖}_{n}$. If the standard factorization of $M$ into primes is $M={q}_{1}^{{\alpha }_{1}}{q}_{2}^{{\alpha }_{2}}...{q}_{k}^{{\alpha }_{k}}$, we define $\ell \left(M\right)$ to be ${q}_{1}^{{\alpha }_{1}}+{q}_{2}^{{\alpha }_{2}}+...+{q}_{k}^{{\alpha }_{k}}$; one century ago, E. Landau proved that $g\left(n\right)={max}_{\ell \left(M\right)\le n}M$ and that, when $n$ goes to infinity, $logg\left(n\right)\sim \sqrt{nlog\left(n\right)}$.There exists a basic algorithm to compute $g\left(n\right)$ for $1\le n\le N$; its running time is $𝒪\left({N}^{3/2}/\sqrt{logN}\right)$ and the needed memory is $𝒪\left(N\right)$; it allows computing $g\left(n\right)$ up to, say, one million. We describe an algorithm to calculate $g\left(n\right)$ for $n$ up to ${10}^{15}$. The main idea is to use the so-called $\ell$-superchampion numbers. Similar numbers, the superior highly composite numbers, were introduced by S. Ramanujan to study large values of the divisor function $\tau \left(n\right)={\sum }_{d\phantom{\rule{0.166667em}{0ex}}|\phantom{\rule{0.166667em}{0ex}}n}1$.

## How to cite

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Deléglise, Marc, Nicolas, Jean-Louis, and Zimmermann, Paul. "Landau’s function for one million billions." Journal de Théorie des Nombres de Bordeaux 20.3 (2008): 625-671. <http://eudml.org/doc/10854>.

@article{Deléglise2008,
abstract = {Let $\{\mathfrak\{S\}\}_n$ denote the symmetric group with $n$ letters, and $g(n)$ the maximal order of an element of $\{\mathfrak\{S\}\}_n$. If the standard factorization of $M$ into primes is $M=q_1^\{\alpha _1\}q_2^\{\alpha _2\}\ldots q_k^\{\alpha _k\}$, we define $\ell (M)$ to be $q_1^\{\alpha _1\}+q_2^\{\alpha _2\}+\ldots +q_k^\{\alpha _k\}$; one century ago, E. Landau proved that $g(n)=\max _\{\ell (M)\le n\} M$ and that, when $n$ goes to infinity, $\log g(n) \sim \sqrt\{n\log (n)\}$.There exists a basic algorithm to compute $g(n)$ for $1 \le n \le N$; its running time is $\mathcal\{O\}\left(N^\{3/2\}/\sqrt\{\log N\}\right)$ and the needed memory is $\mathcal\{O\}(N)$; it allows computing $g(n)$ up to, say, one million. We describe an algorithm to calculate $g(n)$ for $n$ up to $10^\{15\}$. The main idea is to use the so-called $\ell$-superchampion numbers. Similar numbers, the superior highly composite numbers, were introduced by S. Ramanujan to study large values of the divisor function $\tau (n)=\sum _\{d\,|\,n\} 1$.},
affiliation = {Université de Lyon, Université de Lyon 1, CNRS, Institut Camille Jordan, Bât. Doyen Jean Braconnier, 21 Avenue Claude Bernard, F-69622 Villeurbanne cedex, France.; Université de Lyon, Université de Lyon 1, CNRS, Institut Camille Jordan, Bât. Doyen Jean Braconnier, 21 Avenue Claude Bernard, F-69622 Villeurbanne cedex, France.; Centre de Recherche INRIA Nancy Grand Est Projet CACAO -bâtiment A 615 rue du Jardin Botanique, F-54602 Villers-lès-Nancy cedex, France.},
author = {Deléglise, Marc, Nicolas, Jean-Louis, Zimmermann, Paul},
journal = {Journal de Théorie des Nombres de Bordeaux},
keywords = {Arithmetical function; symmetric group; maximal order; highly composite number; arithmetical function; highly composite function; Landau's function},
language = {eng},
number = {3},
pages = {625-671},
publisher = {Université Bordeaux 1},
title = {Landau’s function for one million billions},
url = {http://eudml.org/doc/10854},
volume = {20},
year = {2008},
}

TY - JOUR
AU - Deléglise, Marc
AU - Nicolas, Jean-Louis
AU - Zimmermann, Paul
TI - Landau’s function for one million billions
JO - Journal de Théorie des Nombres de Bordeaux
PY - 2008
PB - Université Bordeaux 1
VL - 20
IS - 3
SP - 625
EP - 671
AB - Let ${\mathfrak{S}}_n$ denote the symmetric group with $n$ letters, and $g(n)$ the maximal order of an element of ${\mathfrak{S}}_n$. If the standard factorization of $M$ into primes is $M=q_1^{\alpha _1}q_2^{\alpha _2}\ldots q_k^{\alpha _k}$, we define $\ell (M)$ to be $q_1^{\alpha _1}+q_2^{\alpha _2}+\ldots +q_k^{\alpha _k}$; one century ago, E. Landau proved that $g(n)=\max _{\ell (M)\le n} M$ and that, when $n$ goes to infinity, $\log g(n) \sim \sqrt{n\log (n)}$.There exists a basic algorithm to compute $g(n)$ for $1 \le n \le N$; its running time is $\mathcal{O}\left(N^{3/2}/\sqrt{\log N}\right)$ and the needed memory is $\mathcal{O}(N)$; it allows computing $g(n)$ up to, say, one million. We describe an algorithm to calculate $g(n)$ for $n$ up to $10^{15}$. The main idea is to use the so-called $\ell$-superchampion numbers. Similar numbers, the superior highly composite numbers, were introduced by S. Ramanujan to study large values of the divisor function $\tau (n)=\sum _{d\,|\,n} 1$.
LA - eng
KW - Arithmetical function; symmetric group; maximal order; highly composite number; arithmetical function; highly composite function; Landau's function
UR - http://eudml.org/doc/10854
ER -

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