Number reference
47 explained.
47: forty-seven, prime; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- forty-seven
- Classification
- prime
- Factors
- 1, 47
- Prime factorization
- 47
- Square root
- 6.855655
- Cube root
- 3.608826
- Binary
- 101111
- Octal
- 57
- Hexadecimal
- 2F
- Roman numeral
- XLVII
- Digit sum
- 11
- Digital root
- 2
What makes 47 notable
- Prime. 47 is prime: it has exactly two divisors, 1 and itself, so it cannot be split into equal whole-number groups any other way.
47 in everyday use
Forty-seven is the atomic number of silver, and the AK-47 rifle takes its number from 1947, the year Mikhail Kalashnikov finished its design. Japan's story of the 47 Ronin, samurai who avenged their master in 1703, is retold in countless plays and films. At Pomona College in California 47 has been a running joke since 1964, and alumni among the writers of Star Trek slipped the number into episode after episode.
Forty-seven is the fifteenth prime and a safe prime, since (47 − 1) / 2 = 23 is also prime, a property valued in cryptography. It is a Lucas number, the sum of 18 and 29 in the sequence that starts 2, 1, 3, 4, 7. It is not a sum of two squares, because it leaves a remainder of 3 when divided by 4. In binary it is 101111.
Nearby numbers
How to read this page
Because 47 is prime, the factor list stops at 1 and 47 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 47 in its prime factorisation inherits it from here.
Percentage calculator · Fraction calculator · Browse Number Explorer