55 (number)

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54 55 56
Cardinal fifty-five
Ordinal 55th
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.


55 is the 10th Fibonacci number and a triangular number (the sum of the numbers 1 to 10). 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) as well as a heptagonal number, and a centered nonagonal number.

In base 10, it is a Kaprekar number.

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).

55 is also the sum of consecutive numbers from 1 to 10.




  • A song produced by Group X was called "Schfifty Five".
  • The name of a song by British Indie Rock Band Kasabian. The song was released as a B side to Club Foot and was recorded live when the band performed at London's Brixton Academy.
  • I Can't Drive 55, a song by Sammy Hagar
  • Ol' '55, a song by Tom Waits
  • Cristian Vogel released an album in 2005 with the title "Station 55"
  • Ol' 55 (band), an Australian rock band.
  • Primer 55 an American band
  • 55 Cadillac, an album by Andrew W.K.




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