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215 (number)

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Title: 215 (number)  
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215 (number)

214 215 216
Cardinal two hundred fifteen
Ordinal 215th
(two hundred and fifteenth)
Factorization 5 × 43
Divisors 5, 43
Roman numeral CCXV
Binary 110101112
Ternary 212223
Quaternary 31134
Quinary 13305
Senary 5556
Octal 3278
Duodecimal 15B12
Hexadecimal D716
Vigesimal AF20
Base 36 5Z36

215 (two hundred and fifteen) is the natural number following 214 and preceding 216.

In mathematics

  • 215 is a composite number and a semiprime.
  • 215 = (3!)^3 - 1
  • 215 is the second smallest integer (after 5) such that n^2-17 is twice a square: 215^2-17 = 2 \times 152^2\, .[1]
  • There are 215 sequences of four integers, counting re-arrangements as distinct, such that the sum of their reciprocals is 1.[2] These are
    • 24 arrangements of (2,3,7,42), (2,3,8,24), (2,3,9,18), (2,3,10,15), (2,4,5,20) and (2,4,6,12).
    • 12 arrangements of (3,3,4,12), (3,4,4,6), (2,3,12,12), (2,4,8,8) and (2,5,5,10).
    • 6 arrangements of (3,3,6,6).
    • 4 arrangements of (2,6,6,6).
    • 1 arrangement of (4,4,4,4).

In other fields

215 is also:

References

  1. ^ (sequence A144796 in OEIS)
  2. ^ (sequence A002967 in OEIS)


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