PowerMod

PowerMod[a, b, m] gives a^b mod m efficiently.

PowerMod[a, -1, m] finds the modular inverse of a modulo m.

Examples

Compute power modulo:

PowerMod[2, 10, 1000]
(* 24 *)

Modular inverse:

PowerMod[3, -1, 7]
(* 5 *)

Verify the inverse:

Mod[3 * 5, 7]
(* 1 *)

Please visit the official Wolfram Language Reference for more details.