45 (number)

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← 44 45 46 →
Cardinal forty-five
Ordinal 45th
(forty-fifth)
Factorization 32× 5
Divisors 1, 3, 5, 9, 15, 45
Greek numeral ΜΕ´
Roman numeral XLV
Binary 1011012
Ternary 12003
Quaternary 2314
Quinary 1405
Senary 1136
Octal 558
Duodecimal 3912
Hexadecimal 2D16
Vigesimal 2520
Base 36 1936

45 (forty-five) is the natural number following 44 and followed by 46.

In mathematics[edit]

Forty-five is a triangular number, and in particular the sum of all the decimal digits (0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45).[1] It is the smallest triangle number (after 1) which can be written as the sum of two squares, it is also a hexagonal[2] and 16-gonal number.[3]

45 is the sixth positive integer with a prime factorization of the form p2q, with p and q being prime.

Since the greatest prime factor of 452 + 1 = 2026 is 1013, which is much more than 45 twice, 45 is a Størmer number.[4]

In base 10, it is a Kaprekar number[5] and a Harshad number.[6]

In science[edit]

Astronomy[edit]

In music[edit]

In other fields[edit]

Forty-five may also refer to:

References[edit]

  1. ^ "Sloane's A000217 : Triangular numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30. 
  2. ^ "Sloane's A000384 : Hexagonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30. 
  3. ^ "Sloane's A051868 : 16-gonal numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30. 
  4. ^ "Sloane's A005528 : Størmer numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30. 
  5. ^ "Sloane's A006886 : Kaprekar numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30. 
  6. ^ "Sloane's A005349 : Niven (or Harshad) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-30. 
  7. ^ Arthur Hill Cash (2007), John Wilkes: The Scandalous Father of Civil Liberty, Yale University Press, p. 219, ISBN 978-0-300-12363-0