91 (number)

Last updated
90 91 92
Cardinal ninety-one
Ordinal 91st
(ninety-first)
Factorization 7 × 13
Divisors 1, 7, 13, 91
Greek numeral ϞΑ´
Roman numeral XCI, xci
Binary 10110112
Ternary 101013
Senary 2316
Octal 1338
Duodecimal 7712
Hexadecimal 5B16

91 (ninety-one) is the natural number following 90 and preceding 92.

Contents

In mathematics

91 is a square pyramidal number. Square-pyramidal-91.png
91 is a square pyramidal number.
91 is a centered hexagonal number. Centered-hexagonal-91.png
91 is a centered hexagonal number.
91 as the sum and difference of two positive cubes Cube-sum-diff-91.png
91 as the sum and difference of two positive cubes

91 is:

The decimal equivalent of the fraction 191 can be obtained by using powers of 9.

In science

References

  1. Sloane, N. J. A. (ed.). "SequenceA001358". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  2. "A000217 - OEIS". oeis.org. Retrieved 2024-11-28.
  3. "Sloane's A000384 : Hexagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
  4. "Sloane's A003215 : Hex (or centered hexagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
  5. "Sloane's A060544 : Centered 9-gonal (also known as nonagonal or enneagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
  6. "Sloane's A005898 : Centered cube numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
  7. "Sloane's A000330 : Square pyramidal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
  8. Sloane, N. J. A. (ed.). "SequenceA047696(Smallest positive number that can be written in n ways as a sum of two (not necessarily positive) cubes.)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  9. Friedman, Erich. What's Special About This Number? Archived 2018-02-23 at the Wayback Machine
  10. "Sloane's A005043 : Riordan numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
  11. "John Conway proves that 91 is the smallest number which looks prime but isn't". Ryan Andersen. 31 December 2020. Retrieved 2024-05-09.
  12. "Prime Numbers". 9 May 2024.