131
Iodine-131 is the isotope released in reactor accidents.
- Odd
- Prime
Where 131 fits
Why 131 is special
It concentrates in the thyroid and has an eight-day half-life, which is why potassium iodide is distributed quickly or not at all.
131 is part of
Factors & digit properties
- Divisors (2)
- 1, 131
- Prime factorisation
- 131
- Digit sum
- 5
- Digital root
- 5
Representations
- Decimal
- 131
- Binary
- 10000011
- Octal
- 203
- Hexadecimal
- 83
- Roman numeral
- CXXXI
- Scientific notation
- 1.310 × 10^2
Other mathematical patterns
- Palindromic number
- Deficient number
- Sophie Germain prime
Related numbers & connections
Both are released in reactor accidents, one determining the immediate response and one the length of the exclusion.
View 137 →Numbers Around Us
- appears alongside137
why?
Strength 0.50, confidence "high".
Science
Iodine-131 has a half-life of about eight days and concentrates in the thyroid gland. Stable iodine prophylaxis saturates the gland and is effective only if given close to exposure.
DocumentedScienceGeography: GlobalPeriod: 1938–
Common questions
Is 131 a prime number?
Yes, 131 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 131?
The factors of 131 are 1, 131.
What is 131 in Roman numerals?
131 in Roman numerals is CXXXI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 3 August 2026