61
61 is a prime number, the atomic number of promethium — the only lanthanide with no stable isotopes — sitting directly after 60.
- Odd
- Prime
Where 61 fits
Why 61 is special
61 is the mirror image of 59 across 60: the first prime after it, just as 59 is the last prime before it.
61 is part of
Factors & digit properties
- Divisors (2)
- 1, 61
- Prime factorisation
- 61
- Digit sum
- 7
- Digital root
- 7
Representations
- Decimal
- 61
- Binary
- 111101
- Octal
- 75
- Hexadecimal
- 3d
- Roman numeral
- LXI
- Scientific notation
- 6.100 × 10^1
Other mathematical patterns
- Deficient number
- Twin prime
Related numbers & connections
59 and 61 are twin primes — two primes exactly two apart.
View 59 →Shares a distinctive class
- is associated with59
why?
Strength 0.50, confidence "high".
Science
61 is the atomic number of promethium, the only lanthanide element with no stable isotopes.
DocumentedScience
Mathematics
61 is prime, sitting directly after the highly composite number 60.
DocumentedMathematics
Common questions
Is 61 a prime number?
Yes, 61 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 61?
The factors of 61 are 1, 61.
What is 61 in Roman numerals?
61 in Roman numerals is LXI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026