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 "" for 3 or "" for 7. This "" can be considered a swash variant of "". The use of a final "" is still used in medical prescriptions to prevent tampering with or misinterpretation of a number after it is written. Numerals in documents and inscriptions from the Middle Ages sometimes include additional symbols, which today are called "medieval Roman numerals". Some simply substitute another letter for the standard one (such as "" for "", or "" for ""), while others serve as abbreviations for compound numerals ("" for "", or "" for ""). Although they are still listed