Number reference
666 explained.
666: six hundred sixty-six, composite, triangular number; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- six hundred sixty-six
- Classification
- composite
- Factors
- 1, 2, 3, 6, 9, 18, 37, 74, 111, 222, 333, 666
- Prime factorization
- 2 × 3 × 3 × 37
- Square root
- 25.806976
- Cube root
- 8.732892
- Binary
- 1010011010
- Octal
- 1232
- Hexadecimal
- 29A
- Roman numeral
- DCLXVI
- Digit sum
- 18
- Digital root
- 9
What makes 666 notable
- Triangular number. 666 is the 36th triangular number: it is the sum 1 + 2 + … + 36, the count of items in a triangle with 36 rows.
- Repdigit. 666 is written with a single repeated digit, so it is divisible by the repunit of the same length.
666 in everyday use
Six hundred sixty-six appears in the Book of Revelation as the "number of the beast", which is why it carries superstition far out of proportion to its arithmetic.
Nearby numbers
How to read this page
The factor list shows every way 666 splits into equal whole-number groups — 12 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 666 for contexts that do not use decimal.
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