21 (عدد)

21 (واحد وعشرون) هو عدد صحيح. says: "ℕ is the set of natural numbers (positive integers)" (p. 3) include zero in the natural numbers: "Intuitively, the set  of all "natural numbers" may be described as follows:  contains an "initial" number 0; ...". They follow that with their version of the Peano Postulates. (p. 15) يلي العدد 20 ويسبق العدد 22 وهو عدد طبيعي موجب.

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تصنيف:أعداد صحيحة