21497917 has 6 divisors (see below), whose sum is σ = 25007838. Its totient is φ = 18426744.

The previous prime is 21497897. The next prime is 21497921. The reversal of 21497917 is 71979412.

It can be written as a sum of positive squares in only one way, i.e., 20196036 + 1301881 = 4494^2 + 1141^2 .

It is not a de Polignac number, because 21497917 - 2¹⁵ = 21465149 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21497917.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21497977) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 219318 + ... + 219415.

It is an arithmetic number, because the mean of its divisors is an integer number (4167973).

Almost surely, 2^21497917 is an apocalyptic number.

It is an amenable number.

21497917 is a deficient number, since it is larger than the sum of its proper divisors (3509921).

21497917 is an equidigital number, since it uses as much as digits as its factorization.

21497917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 438747 (or 438740 counting only the distinct ones).

The product of its digits is 31752, while the sum is 40.

The square root of 21497917 is about 4636.5846266406. The cubic root of 21497917 is about 278.0559080490.

The spelling of 21497917 in words is "twenty-one million, four hundred ninety-seven thousand, nine hundred seventeen".