Number reference
7 explained.
7: seven, prime, mersenne prime; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- seven
- Classification
- prime
- Factors
- 1, 7
- Prime factorization
- 7
- Square root
- 2.645751
- Cube root
- 1.912931
- Binary
- 111
- Octal
- 7
- Hexadecimal
- 7
- Roman numeral
- VII
- Digit sum
- 7
- Digital root
- 7
What makes 7 notable
- Prime. 7 is prime: it has exactly two divisors, 1 and itself, so it cannot be split into equal whole-number groups any other way.
- Mersenne prime. 7 = 2^3 − 1 and is prime, making it a Mersenne prime. These are the primes that large prime searches concentrate on.
7 in everyday use
Seven is the number of days in a week, a convention inherited from Babylonian astronomy and carried into the Hebrew, Greek, and Roman calendars.
Nearby numbers
How to read this page
Because 7 is prime, the factor list stops at 1 and 7 itself, so it cannot be shared into equal whole-number groups. That is also what makes it useful as a building block: every larger number with 7 in its prime factorisation inherits it from here.
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