THC Science

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

In mathematics

215 is a composite number and a semiprime ( $=5\times 43$ ).
$215=(3!)^{3}-1$ .
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]
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).