21257257 has 16 divisors (see below), whose sum is σ = 25709440. Its totient is φ = 17169408.

The previous prime is 21257251. The next prime is 21257273. The reversal of 21257257 is 75275212.

It is a cyclic number.

It is not a de Polignac number, because 21257257 - 2¹¹ = 21255209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21257251) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36553 + ... + 37129.

It is an arithmetic number, because the mean of its divisors is an integer number (1606840).

Almost surely, 2^21257257 is an apocalyptic number.

It is an amenable number.

21257257 is a deficient number, since it is larger than the sum of its proper divisors (4452183).

21257257 is a wasteful number, since it uses less digits than its factorization.

21257257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 880.

The product of its digits is 9800, while the sum is 31.

The square root of 21257257 is about 4610.5592936215. The cubic root of 21257257 is about 277.0144396805.

The spelling of 21257257 in words is "twenty-one million, two hundred fifty-seven thousand, two hundred fifty-seven".