Gematria /ɡəˈmeɪ.tri.ə/ originated as an Assyro-Babylonian-Greek system of alphanumeric code/cipher later adopted into Jewish culture that assigns numerical value to a word/name/phrase in the belief that words or phrases with identical numerical values bear some relation to each other or bear some relation to the number itself as it may apply to Nature, a person's age, the calendar year, or the like.

Similar systems, some of which were derived from or inspired by Hebrew gematria, have been used in other languages and cultures, i.e. Greek isopsephy, Arabicabjad numerals and 'Simple(6,74) English(7,74) Gematria(8,74)'.

The best-known example of Hebrew gematria is the word Chai ("alive"), which is composed of two letters that (using the assignments in the Mispar gadol table shown below) add up to 18. This has made 18 a "lucky number" among Jews, and gifts in multiples of 18 are very popular.

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