55 (number)

For other uses, see 55 (disambiguation).
54 55 56
Cardinal fifty-five
Ordinal 55th
(fifty-fifth)
Factorization 5 × 11
Divisors 1, 5, 11, 55
Roman numeral LV
Binary 1101112
Ternary 20013
Quaternary 3134
Quinary 2105
Senary 1316
Octal 678
Duodecimal 4712
Hexadecimal 3716
Vigesimal 2F20
Base 36 1J36

55 (fifty-five) is the natural number following 54 and preceding 56.

Mathematics

55 is the 10th Fibonacci number[1] and a triangular number (the sum of the consecutive numbers 1 to 10).[2] It is the largest Fibonacci number to also be a triangular number.

It is a square pyramidal number (the sum of the squares of the integers 1 to 5)[3] as well as a heptagonal number,[4] and a centered nonagonal number.[5]

In base 10, it is a Kaprekar number.[6]

55 is a semiprime, being the product of 5 and 11 and it is the 2nd member of the (5.q) semiprime family. 55 is one of only two integers with an aliquot sum of 17 (the other being 39). 55 has an aliquot sequence of 4 members: (55, 17, 1, 0).

Science

Astronomy

Music

Transportation

Film

Years

Other uses

See also

References

  1. "Sloane's A000045 : Fibonacci numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  2. "Sloane's A000217 : Triangular numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  3. "Sloane's A000330 : Square pyramidal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  4. "Sloane's A000566 : Heptagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  5. "Sloane's A060544 : Centered 9-gonal (also known as nonagonal or enneagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
  6. "Sloane's A006886 : Kaprekar numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30.
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