65 (number)

64 65 66
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Cardinal sixty-five
Ordinal 65th
(sixty-fifth)
Factorization 5 × 13
Divisors 1, 5, 13, 65
Roman numeral LXV
Binary 10000012
Ternary 21023
Quaternary 10014
Quinary 2305
Senary 1456
Octal 1018
Duodecimal 5512
Hexadecimal 4116
Vigesimal 3520
Base 36 1T36

65 (sixty-five) is the natural number following 64 and preceding 66.

In mathematics

Sixty-five is the 23rd[1] semiprime and the 3rd of the form (5.q). It is an octagonal number.[2] It is also a Cullen number.[3] Given 65, the Mertens function returns 0.[4]

This number is the magic constant of 5 by 5 normal magic square:

This number is also the magic constant of n-Queens Problem for n = 5.[5]

65 is the smallest integer that can be expressed as a sum of two distinct positive squares in two ways, 65 = 82 + 12 = 72 + 42.

It appears in the Padovan sequence, preceded by the terms 28, 37, 49 (it is the sum of the first two of these).[6]

There are only 65 known Euler's idoneal numbers.

65 = 15 + 24 + 33 + 42 + 51.

65 is the length of the hypotenuse of 4 different pythagorean triangles, the lowest number to have more than 2: 652 = 162 + 632 = 332 + 562 = 392 + 522 = 252 + 602. The first two are "primitive", and 65 is the lowest number to be the largest side of more than one such triple.

In science

Astronomy

In music

In other fields

Sixty-five is:

In sports

References

  1. (sequence A001358 in the OEIS)
  2. "Sloane's A000567 : Octagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  3. "Sloane's A002064 : Cullen numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  4. "Sloane's A028442 : Numbers n such that Mertens' function is zero". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  5. "Sloane's A006003". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  6. "Sloane's A000931 : Padovan sequence". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
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