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词条 215 (number)
释义

  1. In mathematics

  2. In other fields

  3. References

{{refimprove|date=August 2012}}{{Infobox number
| number = 215
| divisor= 5, 43
}}

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 is the second smallest integer (after 5) such that is twice a square: .[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 Oenone is a main belt asteroid.
  • E215 is the E number of Sodium ethyl para-hydroxybenzoate.
  • There are several highways numbered 215.

215 is also:

  • The Dewey Decimal Classification for Science and religion.
  • The year AD 215 or 215 BC
  • 215 is often used as slang for marijuana, from California Proposition 215, legalizing it for medical use.
  • The first area code of metropolitan Philadelphia, Pennsylvania

References

1. ^{{OEIS|A144796}}
2. ^{{OEIS|A002967}}
{{Integers|2}}{{Num-stub}}Nombre 210#Nombres del 211 al 219

1 : Integers
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