## Abstract

The classical Waring problem deals with expressing every natural number as a sum of g(k) kth powers. Similar problems for finite simple groups were studied recently, and in this paper we study them for finite quasisimple groups G. We show that for a fixed group word w≠1 and for G of sufficiently large order we have w(G)^{3}=G, namely every element of G is a product of three values of w. For various families of finite quasisimple groups, including covers of alternating groups, we obtain a stronger result, namely w(G)^{2}=G. However, in contrast with the case of simple groups studied in [14], we show that w(G)^{2}=G need not hold for all large G; moreover, if k>2, then x^{k}y^{k} is not surjective on infinitely many finite quasisimple groups. The case k=2 turns out to be exceptional. Indeed, our last result shows that every element of a finite quasisimple group is a product of two squares. This can be regarded as a noncommutative analog of Lagrange's four squares theorem.

Original language | American English |
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Pages (from-to) | 2323-2348 |

Number of pages | 26 |

Journal | International Mathematics Research Notices |

Volume | 2013 |

Issue number | 10 |

DOIs | |

State | Published - 1 Jan 2013 |

### Bibliographical note

Funding Information:This research was partially supported by NSF grants DMS-0800705 and DMS-1101424 (to M.L.), by the ERC Advanced grant 247034 (to A.S.), by a Bi-National Science Foundation United States-Israel grant 2008194 (to M.L. and A.S.). and also by NSF grant DMS-0901241 (to P.H.T.).