The vigesimal or base 20 numeral system is based on twenty (in the same way in which the decimal numeral system is based on ten).
base 26
base 26 is a positional numeral system with twenty-six as its base. It uses 26 different digits for representing numbers. The digits for base 26 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, and p.