On the semigroups of order-decreasing finite full transformations

Abstract

Synopsis Let Sing n be the subsemigroup of singular elements of the full transformation semigroup on a totally ordered finite set with n elements. Let be the subsemigroup of all decreasing maps of Sing n . In this paper it is shown that is a non-regular abundant semigroup with n − 1 -classes and . Moreover, is idempotent-generated and it is generated by the n ( n − 1)/2 idempotents in J* n−1 . Let and Some recurrence relations satisfied by J*(n, r) and sh (n, r) are obtained. Further, it is shown that sh ( n, r ) is the complementary signless (or absolute) Stirling number of the first kind.