217 (number)217 is the natural number following 216 and preceding 218.In mathematics217 is a centered [hexagonal number], a 12-gonal number, a centered [polygonal number|centered 36-gonal number], a Fermat pseudoprime to base 5, and a Blum integer. It is both the sum of two positive cubes and the difference of two positive consecutive cubes in exactly one way:. When written in binary, it is a non-repetitive Kaprekar number. It is also the sum of all the divisors of and the number of week-month combinations in the Gregorian calendar.