Algorithmic Numeral · entry 667 Algorithmic encodings for 667. Adjacent 666 · 668 T9 keypad MNO MNO PQRS T9 phone-keypad letter set per digit Leet GGT leet substitution: 0=O, 1=I, 3=E, 4=A, 5=S, 7=T, etc. Math 23 × 29 prime factorization Previous 666 668 Next