21317 has 2 divisors, whose sum is σ = 21318. Its totient is φ = 21316.

The previous prime is 21313. The next prime is 21319. The reversal of 21317 is 71312.

It is a Cunningham number, because it is equal to 146²+1.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21316 + 1 = 146^2 + 1^2 .

It is a cyclic number.

It is not a de Polignac number, because 21317 - 2² = 21313 is a prime.

Together with 21319, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21317.

It is not a weakly prime, because it can be changed into another prime (21313) 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 as a sum of consecutive naturals, namely, 10658 + 10659.

It is an arithmetic number, because the mean of its divisors is an integer number (10659).

2²¹³¹⁷ is an apocalyptic number.

It is an amenable number.

21317 is a deficient number, since it is larger than the sum of its proper divisors (1).

21317 is an equidigital number, since it uses as much as digits as its factorization.

21317 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 42, while the sum is 14.

The square root of 21317 is about 146.0034246174. The cubic root of 21317 is about 27.7273711039.

Adding to 21317 its reverse (71312), we get a palindrome (92629).

The spelling of 21317 in words is "twenty-one thousand, three hundred seventeen", and thus it is an iban number.