BitNot[n] gives the bitwise NOT of the integer n.
Integer mathematical function (see Section A.3.10).
BitNot[n] turns ones into zeros and vice versa in the binary bit representation of n.
Integers are assumed to be represented in two's complement form, with an unlimited number of digits, so that BitNot[n] is simply equivalent to .
See The Mathematica Book: Section 3.2.4.
See also: BitAnd, BitOr, BitXor, Not.