Functions relating real numbers and integers. Extracting integer and fractional parts. IntegerPart[x] and FractionalPart[x] can be thought of as extracting digits to the left ...

Rational is the head used for rational numbers.

DigitQ[string] yields True if all the characters in the string are digits in the range 0 through 9, and yields False otherwise.

Mathematica makes it easy to "bulletproof" packages, and prevent features of their environment from affecting their internal operation.

RealExponent[x] gives log_10 (|x|).RealExponent[x, b] gives log_b (|x|).

PaddedForm[expr, n] prints with all numbers in expr padded to leave room for a total of n digits. PaddedForm[expr, {n, f}] prints with approximate real numbers having exactly ...

Two decades of intense R&D at Wolfram Research have given Mathematica by far the world's broadest and deepest coverage of special functions—and greatly expanded the whole ...

 

Testing for numeric quantities. Pi is a symbol, so Pi+3 is not explicitly a number. It does however have a numerical value.

ZeroTest is an option to various linear algebra functions that gives a function to use in testing whether symbolic expressions should be treated as zero.