Thematic
Natural numbers - integers, positive: \[1, 2, 3, 4, 5, 6,... \]
Sometimes it is assumed that the natural numbers should also be the number of zero (authors of mathematical books should always clearly defined, or they recognize the number zero is natural or not).
The set of natural numbers is denoted by the letter \(\mathbb{N} \).
We can write that: \[\mathbb{N} =\left \lbrace 1, 2, 3, 4, 5, 6, ... \right \rbrace\] If we assume also that the zero is a natural number, then write down: \[\mathbb{N} =\left \lbrace 0, 1, 2, 3, 4, 5, ... \right \rbrace\] Sometimes the set of natural numbers we use positive identification \(\mathbb{N}_{+} \). \[\mathbb{N}_{+} =\left \lbrace 1, 2, 3, 4, 5, 6, ... \right \rbrace\] The same set can also save by using the symbol of integers: \[\mathbb{Z}_{+} =\left \lbrace 1, 2, 3, 4, 5, 6, ... \right \rbrace\]
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Integers