FromFiniteField

FromFiniteField[a, ff] converts the element a of the prime subfield of the finite field ff to an integer.

FromFiniteField[expr, ff, t] converts the elements of the finite field ff in the coefficients of the rational expression expr to polynomials in t, where t represents the field generator.

Examples

ff = FiniteField[5];
FromFiniteField[ff[3], ff]
(* 3 *)

Please visit the official Wolfram Language Reference for more details.