215 (number)

← 214 215 216 →
← 200 210 220 230 240 250 260 270 280 290 → List of numbers — Integers ← 0 100 200 300 400 500 600 700 800 900 →
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 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. (sequence A144796 in OEIS)
2. (sequence A002967 in OEIS)