CentralNotice Ordinal number From Wikipedia, the free encyclopedia Jump to: navigation , search This article is about the mathematical concept. For number words denoting a position in a sequence ("first", "second", "third", etc.), see Ordinal number (linguistics) . Representation of the ordinal numbers up to ω ω . Each turn of the spiral represents one power of ω In set theory , an ordinal number , or just ordinal , is the order type of a well-ordered set . They are usually identified with hereditarily transitive sets . Ordinals are an extension of the natural numbers different from integers and from cardinals . Like other kinds of numbers, ordinals can be added, multiplied, and exponentiated. Ordinals were introduced by Georg Cantor in 1883 [ 1 ] to accommodate infinite sequences and to classify derived sets , which he had previously introduced in 1872 while s...