The Ionian or Milesian numerals give each letter a place in three bands: alpha–theta 1–9, iota–koppa 10–90 by tens, rho–omega 100–800 by hundreds, with the obsolete digamma (6), koppa (90) and sampi (900) filling the gaps. θεός = 9+5+70+200 = 284; Ἰησοῦς = 10+8+200+70+400+200 = 888; Ἀβρασάξ = 1+2+100+1+200+1+60 = 365.
Isopsephy is the Greek practice that gematria is named after and the older of the two: the Milesian system was in use by the sixth century BCE, and the practice is Pythagorean in the ancient accounts. The magical papyri use it constantly, both to compose names of power whose number matches a desired outcome and to test whether two names are equal and therefore linked. Basilides' 365 heavens, the 365 of Abrasax and the 888 of Jesus in the Sibylline Oracles are the surviving showpieces.
Every entry that names Isopsephy (Greek letter-values), grouped by the system it comes from.