Syndetic set

In mathematics, a syndetic set is a subset of the natural numbers, having the property of "bounded gaps": that the sizes of the gaps in the sequence of natural numbers is bounded. 
Definition.
A set formula_1 is called syndetic if for some finite subset "F" of formula_2
where formula_4. Thus syndetic sets have "bounded gaps"; for a syndetic set formula_5, there is an integer formula_6 such that formula_7 for any formula_8.