21217 has 6 divisors (see below), whose sum is σ = 24738. Its totient is φ = 18144.

The previous prime is 21211. The next prime is 21221. The reversal of 21217 is 71212.

It can be written as a sum of positive squares in only one way, i.e., 14161 + 7056 = 119^2 + 84^2 .

It is not a de Polignac number, because 21217 - 2⁷ = 21089 is a prime.

It is a super-2 number, since 2×21217² = 900322178, which contains 22 as substring.

It is a nialpdrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 21197 and 21206.

It is not an unprimeable number, because it can be changed into a prime (21211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 168 + ... + 265.

It is an arithmetic number, because the mean of its divisors is an integer number (4123).

2²¹²¹⁷ is an apocalyptic number.

It is an amenable number.

21217 is a deficient number, since it is larger than the sum of its proper divisors (3521).

21217 is an equidigital number, since it uses as much as digits as its factorization.

21217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 447 (or 440 counting only the distinct ones).

The product of its digits is 28, while the sum is 13.

The square root of 21217 is about 145.6605643268. The cubic root of 21217 is about 27.6839459164.

Adding to 21217 its reverse (71212), we get a palindrome (92429).

The spelling of 21217 in words is "twenty-one thousand, two hundred seventeen", and thus it is an iban number.