# 87 (number)

87 (eighty-seven) is the natural number following 86 and preceding 88.

 ← 86 87 88 →
Cardinaleighty-seven
Ordinal87th
(eighty-seventh)
Factorization3 × 29
Divisors1, 3, 29, 87
Greek numeralΠΖ´
Roman numeralLXXXVII
Binary10101112
Ternary100203
Octal1278
Duodecimal7312
Hexadecimal5716

## In mathematics

87 is:

• the sum of the squares of the first four primes (87 = 22 + 32 + 52 + 72).
• the sum of the sums of the divisors of the first 10 positive integers.[1]
• the thirtieth semiprime,[2] and the twenty-sixth distinct semiprime[3] and the eighth of the form (3.q).
• 5! - 4! - 3! - 2! - 1! = 87

## In other fields

Eighty-seven is also:

## References

1. ^ Sloane, N. J. A. (ed.). "Sequence A024916 (sum_{k=1..n} sigma(k) where sigma(n) = sum of divisors of n)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
2. ^ "A001358 - OEIS". oeis.org. Retrieved 2020-08-10.
3. ^ "A006881 - OEIS". oeis.org. Retrieved 2020-08-10.
4. ^ Ferris, Sam (2014-11-02). "The real story behind Australia's unlucky number 87". cricket.com.au. Retrieved 2022-01-27.
5. ^ "Guide to model railroading scales and gauges". Model Railroader. 2 November 2011. Retrieved 2 October 2016.