Noun
(mathematics) The set of positive integers, {1, 2, 3, ...}.
(mathematics, computer science) The set of non-negative integers, {0, 1, 2, 3, ...}.
Source: en.wiktionary.orgHe treated Root exactly as he treated prime numbers. For him, primes were the base on which all other natural numbers relied; and children were the foundation of everything worthwhile in the adult world. Yōko Ogawa
All systems which satisfy the five primitive propositions are in one-to-one correspondence with the natural numbers. Giuseppe Peano