# 215 (number)

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

 ← 214 215 216 →
Cardinaltwo hundred fifteen
Ordinal215th
(two hundred fifteenth)
Factorization5 × 43
Divisors5, 43
Greek numeralΣΙΕ´
Roman numeralCCXV
Binary110101112
Ternary212223
Senary5556
Octal3278
Duodecimal15B12

## In mathematics

• 215 is a composite number and a semiprime.
• ${\displaystyle 215=(3!)^{3}-1}$
• 215 is the second smallest integer (after 5) such that ${\displaystyle n^{2}-17}$  is twice a square: ${\displaystyle 215^{2}-17=2\times 152^{2}}$ .[1]
• 215 is a vertically symmetric number on a calculator display (sequence A053701 in the OEIS).
• 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).

215 is also:

## References

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