215 (number)

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:

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