21757213 has 2 divisors, whose sum is σ = 21757214. Its totient is φ = 21757212.

The previous prime is 21757199. The next prime is 21757243. The reversal of 21757213 is 31275712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13816089 + 7941124 = 3717^2 + 2818^2 .

It is a cyclic number.

It is not a de Polignac number, because 21757213 - 2⁵ = 21757181 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21757243) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10878606 + 10878607.

It is an arithmetic number, because the mean of its divisors is an integer number (10878607).

Almost surely, 2^21757213 is an apocalyptic number.

It is an amenable number.

21757213 is a deficient number, since it is larger than the sum of its proper divisors (1).

21757213 is an equidigital number, since it uses as much as digits as its factorization.

21757213 is an evil number, because the sum of its binary digits is even.

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

The square root of 21757213 is about 4664.4627772124. The cubic root of 21757213 is about 279.1693622769.

The spelling of 21757213 in words is "twenty-one million, seven hundred fifty-seven thousand, two hundred thirteen".