Conjectures on the normal covering number of finite symmetric and alternating groups

Abstract

Let gamma(Sn) be the minimum number of proper subgroups Hi, i = 1,...,ell, of the symmetric group Sn such that each element in Sn lies in some conjugate of one of the Hi. In this paper we conjecture that gamma(Sn) =(n/2)(1-1/p_1) (1-1/p_2) + 2, where p1, p2 are the two smallest primes in the factorization of n and n is neither a prime power nor a product of two primes. Support for the conjecture is given by a previous result for the case where n has at most two distinct prime divisors. We give further evidence by confirming the conjecture for certain integers of the form n = 15q, for an infinite set of primes q, and by reporting on a Magma computation. We make a similar conjecture for gamma(An), when n is even, and provide a similar amount of evidence.

Keywords

• Covering
• symmetric group
• alternating group