• 217 can be written using four 4's:
217 has 4 divisors (see below), whose sum is σ = 256. Its totient is φ = 180.
The previous prime is 211. The next prime is 223. The reversal of 217 is 712.
217 is nontrivially palindromic in base 6 and base 12.
It is a Cunningham number, because it is equal to 63+1.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.
It is an interprime number because it is at equal distance from previous prime (211) and next prime (223).
It is a cyclic number.
It is not a de Polignac number, because 217 - 27 = 89 is a prime.
It is a Duffinian number.
217 is an undulating number in base 12.
It is a plaindrome in base 11, base 13 and base 14.
It is a nialpdrome in base 7, base 8, base 15 and base 16.
It is not an unprimeable number, because it can be changed into a prime (211) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (5) of ones.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9 + ... + 22.
It is an arithmetic number, because the mean of its divisors is an integer number (64).
217 is the 9-th hex number.
It is an amenable number.
217 is a deficient number, since it is larger than the sum of its proper divisors (39).
217 is an equidigital number, since it uses as much as digits as its factorization.
217 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 38.
The product of its digits is 14, while the sum is 10.
The square root of 217 is about 14.7309198627. The cubic root of 217 is about 6.0092450069.
Adding to 217 its product of digits (14), we get a triangular number (231 = T21).
Adding to 217 its reverse (712), we get a palindrome (929).
It can be divided in two parts, 21 and 7, that added together give a triangular number (28 = T7).
The spelling of 217 in words is "two hundred seventeen", and thus it is an aban number and an iban number.
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