666 (number) on 1/149 in base 10 has a magic total of 666. The prime factorization of 666 is 2 • 3 • 37. Also, 666 is the sum of squares of first seven primes: formula_2 The Roman numeral for 666, DCLXVI, has exactly one occurrence of all symbols whose value is less than 1000 in decreasing order (D = 500, C = 100, L = 50, X = 10, V = 5, I = 1). In the Textus Receptus manuscripts of the New Testament, the Book of Revelation () cryptically asserts 666 to be "man's number" or "the number of a
Roman numerals feature of Roman numerals is called subtractive notation. The numbers from 1 to 10 (including subtractive notation for 4 and 9) are expressed in Roman numerals as follows: The system being basically decimal, "tens and hundreds follow the same underlying pattern". This is the key to understanding Roman numerals: Thus 10 to 100 (counting in tens, with taking the place of , taking the place of and taking the place of ): Note that 40 () and 90 () follow the same subtractive pattern as 4 and 9, avoiding the confusing and . Similarly, 100 to 1000 (counting in hundreds):