a symbol denoting/representing a natural number ("a numeral") we'll work with four systems of numerals roman: I, V, X, L, C, D, M decimal: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 binary: 0, 1 hexadecimal: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f other systems of numerals are also possible (e.g. base64)