666 (number)

← 665 666 667 →
List of numbers — Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	six hundred sixty-six
Ordinal	666th (six hundred sixty-sixth)
Factorization	2 × 32× 37
Roman numeral	DCLXVI
Binary	10100110102
Ternary	2202003
Quaternary	221224
Quinary	101315
Senary	30306
Octal	12328
Duodecimal	47612
Hexadecimal	29A16
Vigesimal	1D620
Base 36	II36
Greek numeral	χξϛʹ
Chinese numeral	六百六十六
Arabic numeral	٦٦٦

666 (six hundred sixty-six) is the natural number following 665 and preceding 667.

Six hundred and sixty-six is called the "number of the Beast" in (most manuscripts of) chapter 13 of the Book of Revelation, of the New Testament, and also in popular culture.

666 is the sum of the first 36 natural numbers (${\displaystyle \sum _{i=1}^{36}i}$, i.e. 1 + 2 + 3 + ... + 34 + 35 + 36 = 666), and thus it is a triangular number. Notice that 36 = 15 + 21; 15 and 21 are also triangular numbers; and 15² + 21² = 225 + 441 = 666.

In base 10, 666 is a repdigit (and therefore a palindromic number) and a Smith number. A prime reciprocal magic square based on 1/149 in base 10 has a magic total of 666.

The prime factorization of 666 is 2 • 3² • 37. Also, 666 is the sum of squares of first seven primes: ${\displaystyle 2^{2}+3^{2}+5^{2}+7^{2}+11^{2}+13^{2}+17^{2}}$

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