Khmer numerals are the numerals used in the Khmer language. They have been in use since at least the early 7th century, with the earliest known use being on a stele dated to AD 604 found in Prasat Bayang, near Angkor Borei, Cambodia. Numerals Having been derived from the Hindu numerals, modern Khmer numerals also represent a decimal positional notation system. It is the script with the first extant material evidence of zero as a numerical figure, dating its use back to the seventh century, two centuries before its certain use in India. Old Khmer, or Angkorian Khmer, also possessed separate symbols for the numbers 10, 20, and 100. Each multiple of 20 or 100 would require an additional stroke over the character, so the number 47 was constructed using the 20 symbol with an additional upper stroke, followed by the symbol for number 7. This inconsistency with its decimal system suggests that spoken Angkorian Khmer used a vigesimal system. As both Thai and Lao scripts are derived from Old Khmer, their modern forms still bear many resemblances to the latter, demonstrated in the following table: Modern Khmer numbers The spoken names of modern Khmer numbers represent a biquinary system, with both base 5 and base 10 in use. For example, 6 () is formed from 5 () plus 1 (). Numbers from 0 to 5 With the exception of the number 0, which stems from Sanskrit, the etymology of the Khmer numbers from 1 to 5 is of proto-Austroasiatic origin. For details of the various alternative romanization systems, see Romanization of Khmer. Some authors may alternatively mark as the pronunciation for the word two, and either or for the word three. In neighbouring Thailand the number three is thought to bring good luck. However, in Cambodia, taking a picture with three people in it is considered bad luck, as it is believed that the person situated in the middle will die an early death. Comparison to other Austroasiatic languages 1-5 Whilst Khmer and Vietnamese are very different languages, the numbers 1-5 both retain proto-Austroasiatic origins. Numbers from 6 to 20 The numbers from 6 to 9 may be constructed by adding any number between 1 and 4 to the base number 5 (), so that 7 is literally constructed as 5 plus 2. Beyond that, Khmer uses a decimal base, so that 14 is constructed as 10 plus 4,