Number reference
61 explained.
61: sixty-one, prime; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- sixty-one
- Classification
- prime
- Factors
- 1, 61
- Prime factorization
- 61
- Square root
- 7.81025
- Cube root
- 3.936497
- Binary
- 111101
- Octal
- 75
- Hexadecimal
- 3D
- Roman numeral
- LXI
- Digit sum
- 7
- Digital root
- 7
What makes 61 notable
- Prime. 61 is prime: it has exactly two divisors, 1 and itself, so it cannot be split into equal whole-number groups any other way.
61 in everyday use
Sixty-one is the atomic number of promethium, the only rare-earth element with no stable isotope, named after the Titan who stole fire. Roger Maris hit 61 home runs in 1961, breaking Babe Ruth's single-season record, a mark that stood in the American League until 2022. Bob Dylan's 1965 album Highway 61 Revisited took its title from the road running from his home state of Minnesota down to New Orleans.
Sixty-one is the eighteenth prime and the upper member of the twin pair 59 and 61. It is the sum of two consecutive squares, 25 + 36, which makes it a centered square number: a dot ringed by ever-larger squares. It is also a full-reptend prime, meaning the decimal expansion of 1/61 repeats only after 60 digits, the longest cycle possible. In binary it is 111101.
Nearby numbers
How to read this page
Because 61 is prime, the factor list stops at 1 and 61 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 61 in its prime factorisation inherits it from here.
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