Chai is spelled chet, value 8, and yud, value 10, summing to 18. The equivalence is documented everywhere in practice: charitable gifts in multiples of 18, the toast l'chaim, the chai pendant as standard jewelry. Among the hundreds of gematria equivalences in the tradition, this is the one that escaped the study hall into the marketplace, the single most socially active number-letter equation on earth.
The story as practiced: when the community collects for a wedding, a circumcision, a recovery, the amounts come in chai, 18, 36, 180, because you do not hand someone an abstract quantity, you hand them life itself, spelled in the only arithmetic the tradition trusts. Double chai, 36, is the legend-keeper's number too: the lamed-vav tzadikim, the 36 hidden righteous who hold up the world in each generation.
The claim: chai is not superstition but memory engineering. A dispersed people with no territory needed portable rituals, and a number-letter equation is the most portable ritual there is: it survives translation, exile, and currency change, because it lives in the alphabet itself. On this reading, gematria's real function was never prophecy but continuity, a checksum for identity.
Is a gift of 180 dollars eighteen or is it life, and does the number care what you call it?