FromDigits

FromDigits[list] constructs an integer from the list of its decimal digits.

FromDigits[list, b] takes the digits to be given in base b.

Example: FromDigits[3,7,4] .

FromDigits is effectively the inverse of IntegerDigits.

FromDigits[list, n, b] takes n to be an exponent, while FromDigits[list, rep, n, b] takes rep to be repeated, so that FromDigits can also be used as the inverse of RealDigits.

Since IntegerDigits[n] discards the sign of n, FromDigits[IntegerDigits[n]] is Abs[n] not just n.

The digits in list and the base b need not be positive integers, and can be any expression.

If Indeterminate appears in list, it is assumed to signify unknown digits beyond the precision of an approximate real number.

See The Mathematica Book: Section 3.1.3.

See also: IntegerDigits, RealDigits, FromContinuedFraction, NumberForm, DigitCount.