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.