87 (number)

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← 86 87 88 →
Cardinaleighty-seven
Ordinal87th
(eighty-seventh)
Factorization3 × 29
Divisors1, 3, 29, 87
Greek numeralΠΖ´
Roman numeralLXXXVII
Binary10101112
Ternary100203
Senary2236
Octal1278
Duodecimal7312
Hexadecimal5716

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

In mathematics[edit]

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).
  • together with 85 and 86,[4] forms the last semiprime in the 2nd cluster of three consecutive semiprimes; the first comprising 33, 34, 35.
  • with an aliquot sum of 33; itself a semiprime, within an aliquot sequence of five composite numbers (87,33,15,9,4,3,1,0) to the Prime in the 3-aliquot tree.
  • 5! - 4! - 3! - 2! - 1! = 87
  • the last two decimal digits of Graham's number.

In sports[edit]

In other fields[edit]

Eighty-seven is also:

See also[edit]

References[edit]

  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. ^ Sloane, N. J. A. (ed.). "Sequence A056809". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  5. ^ Ferris, Sam (2014-11-02). "The real story behind Australia's unlucky number 87". cricket.com.au. Retrieved 2022-01-27.
  6. ^ "Guide to model railroading scales and gauges". Model Railroader. 2 November 2011. Archived from the original on 22 June 2015. Retrieved 2 October 2016.