Rings and semigroups with permutable zero products

We consider rings R, not necessarily with 1, for which there is a nontrivial permutation sigma on n letters such that x(1)....x(n) = 0 implies x(sigma(1))...x(sigma(n)) = 0 for all x(1), ..., x(n) is an element of R. We prove that this condition alone implies very strong permutability conditions for zero products with sufficiently many factors. To this end we study the infinite sequences of permutation groups P-n (R) consisting of those permutations sigma on n letters for which the condition above is satisfied in R. We give the full characterization of such sequences both for rings and for semigroups with 0. This enables us to generalize some recent results by Cohn on reversible rings and by Lambek, Anderson and Camillo on rings and semigroups whose zero products commute. In particular, we prove that rings with permutable zero products satisfy the Kothe conjecture. (c) 2005 Elsevier B.V. All rights reserved.