21253717 has 4 divisors (see below), whose sum is σ = 21332416. Its totient is φ = 21175020.

The previous prime is 21253711. The next prime is 21253721. The reversal of 21253717 is 71735212.

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 a cyclic number.

It is not a de Polignac number, because 21253717 - 2¹¹ = 21251669 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21253711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 38943 + ... + 39484.

It is an arithmetic number, because the mean of its divisors is an integer number (5333104).

Almost surely, 2^21253717 is an apocalyptic number.

It is an amenable number.

21253717 is a deficient number, since it is larger than the sum of its proper divisors (78699).

21253717 is an equidigital number, since it uses as much as digits as its factorization.

21253717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78698.

The product of its digits is 2940, while the sum is 28.

The square root of 21253717 is about 4610.1753762737. The cubic root of 21253717 is about 276.9990616293. Note that the first 3 decimals are identical.

Adding to 21253717 its reverse (71735212), we get a palindrome (92988929).

The spelling of 21253717 in words is "twenty-one million, two hundred fifty-three thousand, seven hundred seventeen".