Algorithmic Numeral · entry 421 Algorithmic encodings for 421. Adjacent 420 · 422 T9 keypad GHI ABC ⌷ T9 phone-keypad letter set per digit Leet AZI leet substitution: 0=O, 1=I, 3=E, 4=A, 5=S, 7=T, etc. Math prime has no positive divisors other than 1 and itself Previous 420 422 Next