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: ${\displaystyle 217=6^{3}+1^{3}=9^{3}-8^{3}}$ . When written in binary, it is a non-repetitive Kaprekar number.^[2] It is also the sum of all the divisors of 100.

• 217, the year