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In mathematics

217 is a centered hexagonal number, a 12-gonal number, a centered 36-gonal number, a Fermat pseudoprime to base 5, and a Blum integer.¹ It is both the sum of two positive cubes and the difference of two positive consecutive cubes in exactly one way: 217 = 6 3 + 1 3 = 9 3 − 8 3 {\displaystyle 217=6^{3}+1^{3}=9^{3}-8^{3}} . When written in binary, it is a non-repetitive Kaprekar number.² It is also the sum of all the divisors of 100.

See also

• 217, the year

References

1. The Number 217, Virtue Science http://www.virtuescience.com/217.html ↩

2. The non-repetitive Kaprekar binary numbers in decimal, OEIS http://oeis.org/A163205 ↩