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  • IntegerQ[ expr ] gives True if expr is an integer, and False otherwise.
  • IntegerQ[ expr ] returns False unless expr is manifestly an integer (i.e., has head Integer).
  • You can use IntegerQ[ x ] = True to override the normal operation of IntegerQ, and effectively define x to be an integer.
  • See the Mathematica book: Section 2.3.5Section 3.1.1.
  • See also: EvenQ, OddQ, NumberQ, TrueQ.