D'ni number system

The number system of the D'ni is base twenty-five. This means that they have twenty-five digits (0 to 24), and their place value is based on powers of twenty-five.

Though it is a base-25 numeral system, all numerals are derived from five basic glyphs. These glyphs unaltered are the "basic" numerals 0, 1, 2, 3, and 4. The numerals 1, 2, 3, and 4 are rotated ninety degrees counterclockwise to yield the "rotated" numerals 5, 10, 15, and 20, respectively. (Rotating the basic numeral, therefore, multiplies its value by five; this principle of Fives misleads many to believe that D'ni numerals are base-5.)

BTW, there are two ways to write the number twenty-five. It is the only D'ni number which has a dual representation. Twenty-five is usually written with two characters, but in special circumstances it can be written with the single character as well.

Enough talking, for the layman who likes to solve a puzzle, it is usually enough to just look at the chart: