215 (number)

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← 214 215 216 →
Cardinal two hundred fifteen
Ordinal 215th
(two hundred 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[edit]

  • 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[edit]

215 is also:

References[edit]

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