Octadecimal
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| Numeral systems by culture | |
|---|---|
| Hindu-Arabic numerals | |
| Indian Eastern Arabic Khmer |
Indian family Brahmi Thai |
| East Asian numerals | |
| Chinese Suzhou Counting rods |
Japanese Korean |
| Alphabetic numerals | |
| Abjad Armenian Cyrillic Ge'ez |
Hebrew Greek (Ionian) Āryabhaṭa |
| Other systems | |
| Attic Babylonian Egyptian Etruscan |
Mayan Roman Urnfield |
| List of numeral system topics | |
| Positional systems by base | |
| Decimal (10) | |
| 2, 4, 8, 16, 32, 64 | |
| 1, 3, 9, 12, 20, 24, 30, 36, 60, more… | |
Octadecimal or base 18 is a positional numeral system using 18 as the radix. Digits in this base can be represented using the Arabic numerals 0-9 and the Latin letters A-H.
Octadecimal is a rarely used base, though the ancient Mayan calendar is sometimes interpreted as a combination of vigesimal and octadecimal numerical systems - developed in order to match the number of days in a year. There are also some specialised computer systems where octadecimal notation has been used for high levels of data compression. As a base, it has poor radix economy, and because its radix falls between twin primes, there are few recurring fractions with short periods.
| Decimal | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Octadecimal | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | G | H | 10 |
| Decimal | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 |
| Octadecimal | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 1A | 1B | 1C | 1D | 1E | 1F | 1G | 1H | 20 | 21 |
In octadecimal, all prime numbers apart from 2 and 3 will end in 1, 5, 7, B, D or H.
Dont look up there! look here; the numbers go from 0-7 because "..oct..." means 8, and 0 is a diget.!
