87 (number)

An overview of the integer 87: mathematical properties, representations, scientific and cultural appearances, and notable facts.

Overview

87 is a positive integer that lies between 86 and 88. It is an odd, composite number whose prime factorization is 3 × 29. As a product of two primes, 87 is a semiprime. In Roman numerals it is written LXXXVII and in everyday speech it is often read as "eighty-seven."

Mathematical properties

Key arithmetic and number-theoretic facts include:

Divisors: 1, 3, 29 and 87.
Prime factorization: 3 × 29 (two distinct primes).
Number-theoretic functions: it has 4 positive divisors; the sum of divisors is 120 and the Euler totient φ(87) = 56.
Parity: it is an odd number.
Digit properties: in base 10 its digits sum to 8 + 7 = 15, giving a digital root of 6.

Representations

Common numeral-system representations and encodings for 87 include binary 1010111, octal 127, and hexadecimal 0x57. In the ASCII character set the decimal code 87 corresponds to the uppercase letter "W." The trivial divisor 1 is often listed when enumerating factors (1).

Science, history and uses

The atomic number 87 identifies the element francium (symbol Fr), a highly radioactive alkali metal first isolated by Marguerite Perey. The number also appears in everyday contexts such as road and route designations (for example, Interstate 87 in New York) and as a model or product number in manufacturing. In mathematics and computing 87 may appear in examples, benchmarks, or as a parameter value.

Notable facts and distinctions

Because 87 is the product of two distinct primes it is not prime and not a perfect power. It is one of many three-digit combinations in various numeral bases that convert cleanly between binary, octal, and hexadecimal. Its role as the atomic number of francium connects the abstract integer to a concrete place on the periodic table and to the history of chemical discovery.

For further reading and numerical context search general references on integers and prime factorization, or consult resources indexed under the number 87 or related topics such as semiprimes and representations in different bases (neighbors and classifications).