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The negative integers are real integers that are less than 0. For example, –147 and –4 are negative integers, but –0.4181554... and 10 are not (the former is a negative number but not an integer, the latter is a positive integer). The negative integers are listed in A001478, which can be thought of as the "negative equivalent" of A000027.
The absolute value of a negative integer is the number multiplied by –1. The set of all negative integers may be denoted . And so we may write for that .
The study of prime numbers is generally unconcerned with negative integers. But the question does occasionally arise: how do you write the factorization of a negative integer? A number of different solutions suggest themselves, for example, , etc., but these are unsatisfactory on account of the seemingly arbitrary sign choices. To insure uniformity, the factorization of a negative integer could be expressed as –1 followed by the factorization of the absolute value, e.g., .
In the OEIS, if a sequence includes negative numbers it gets the keyword "sign" in the Keywords field (this is mutually exclusive with keyword:nonn). Note that in such OEIS sequence entries, the short dash "-" is used rather than "–"; but since a monospace font is used, this difference becomes relevant only when copying and pasting.