IntegerDigits

IntegerDigits[n] gives a list of the decimal digits in the integer n.

IntegerDigits[n, b] gives the digits in base b.

IntegerDigits[n, b, len] pads the list on the left with zeros to give a list of length len.

Examples

Get decimal digits:

IntegerDigits[12345]
(* {1, 2, 3, 4, 5} *)

Binary representation:

IntegerDigits[42, 2]
(* {1, 0, 1, 0, 1, 0} *)

Pad to fixed length:

IntegerDigits[42, 2, 8]
(* {0, 0, 1, 0, 1, 0, 1, 0} *)

Please visit the official Wolfram Language Reference for more details.