RealDigits[x] gives a list of the digits in the approximate real number x, together with the number of digits that are to the left of the decimal point.
RealDigits[x, b] gives a list of base-b digits in x.
RealDigits[x, b, len] gives a list of len digits.
RealDigits[x, b, len, n] gives len digits starting with the coefficient of .
RealDigits[x] normally returns a list of digits whose length is equal to Precision[x].
RealDigits[x] and RealDigits[x, b] normally require that x be an approximate real number, returned for example by N. RealDigits[x, b, len] also works on exact numbers.
For exact rational numbers RealDigits[x] returns a list of digits of the form , , ... , , , ... representing the digits followed by infinite cyclic repetition of the .
If len is larger than Log[10, b] Precision[x] remaining digits are filled in as Indeterminate.
RealDigits[x, b, len, n] starts with the digit which is the coefficient of , truncating or padding with zeros as necessary.
RealDigits[x, b, len, -1] starts with the digit immediately to the right of the base-b decimal point in x.
The base b in RealDigits[x, b] need not be an integer. For any real b such that , RealDigits[x, b] successively finds the largest integer multiples of powers of b that can be removed while leaving a non-negative remainder.
RealDigits[x] discards the sign of x.
FromDigits can be used as the inverse of RealDigits.
See The Mathematica Book: Section 3.1.3.
See also: MantissaExponent, IntegerDigits, BaseForm, FromDigits, ContinuedFraction, MultiplicativeOrder.