Pentadecimal (base-15) is the positional numeral notation system based on the number fifteen. Comparatively, the decimal system is based on the number ten, the hexadecimal system is based on the number sixteen, and so on. Another name used for the base-15 system is quindecimal (although this term can be confused with quinary, which is a base-5 numeral system).

Pentadecimal requires fifteen symbols. Since there are only ten common decimal digits, the notation can be extended by using letters A, B, C, D and E to represent values 10, 11, 12, 13 and 14, respectively. For example, decimal values 0 to 20 in pentadecimal would be: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, 10, 11, 12, 13, 14, 15. The pentadecimal number 373 would be 783 in decimal.

This numeric base is infrequently used. It finds applications in mathematics as well as fields such as telephony routing over IP (see RFC 3219) and other specialized uses.

## Natural languages

The Huli language of Papua New Guinea is reported to have base-15 numerals. Ngui means 15, ngui ki means 15×2 = 30, and ngui ngui means 15×15 = 225.^{[1]}

## References

- ↑ Cheetham, Brian (1978), "Counting and Number in Huli", Papua New Guinea Journal of Education 14: 16–35