85 (number)

In mathematics

85 is:

• the product of two prime numbers (5 and 17), and is therefore a semiprime of the form (5.q) where q is prime.
• specifically, the 24th Semiprime, it being the fourth of the form (5.q).
• together with 86 and 87, forms the second cluster of three consecutive semiprimes; the first comprising 33, 34, 35.
• with a prime aliquot sum of 23 in the short aliquot sequence (85,23,1,0).
• an octahedral number.
• a centered triangular number.
• a centered square number.
• a decagonal number.
• the smallest number that can be expressed as a sum of two squares, with all squares greater than 1, in two ways, 85 = 92 + 22 = 72 + 62.
• the length of the hypotenuse of four Pythagorean triangles.
• a Smith number in decimal.

In other fields

Note: please do not add things which simply and non-notably have this number of members. For example the number of pages or chapters in a book, episodes or seasons of a series, subdivisions in a state, rockets of a particular type, etc.

• The radix of the Ascii85 (sometimes called Base85) binary-to-text encoding
• Part of the assignation for the Toyota AE85, commonly referred to as an "eight-five".

References

References

1. {{Cite OEIS. A056809. Numbers k such that k, k+1 and k+2 are products of two primes
2. {{Cite OEIS. A005900. Octahedral numbers
3. {{Cite OEIS. A005448. Centered triangular numbers
4. {{Cite OEIS. A001844. Centered square numbers
5. {{Cite OEIS. A001107. 10-gonal (or decagonal) numbers
6. {{Cite OEIS. A007692. Numbers that are the sum of 2 non-zero squares in 2 or more ways. The two smaller numbers on this list, 50 and 65, have 1 as one of the squares in their representations as sums of two squares.
7. {{Cite OEIS. A006753. Smith numbers