Number reference
87 explained.
87: eighty-seven, composite; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- eighty-seven
- Classification
- composite
- Factors
- 1, 3, 29, 87
- Prime factorization
- 3 × 29
- Square root
- 9.327379
- Cube root
- 4.431048
- Binary
- 1010111
- Octal
- 127
- Hexadecimal
- 57
- Roman numeral
- LXXXVII
- Digit sum
- 15
- Digital root
- 6
What makes 87 notable
- Semiprime. 87 = 3 × 29, a product of exactly two primes. That gives it just four divisors, so it splits into equal groups in only two non-trivial ways.
87 in everyday use
Lincoln's Gettysburg Address opens with "four score and seven years ago", which is 87 years, counting back from 1863 to the Declaration of Independence in 1776. Eighty-seven is the atomic number of francium, the most unstable of the first 101 elements, with a longest half-life of 22 minutes. Australian cricketers call 87 the "devil's number", thirteen short of a century, and some batters still fidget when the scoreboard shows it.
Eighty-seven is 3 × 29 and the sum of the squares of the first four primes, 4 + 9 + 25 + 49. Like 51 and 57 it looks prime at a glance but is not. In binary it is 1010111, its digits sum to 15, and its reversal, 78, is a triangular number.
Nearby numbers
How to read this page
The factor list shows every way 87 splits into equal whole-number groups — 4 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 87 for contexts that do not use decimal.
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