21107257 has 4 divisors (see below), whose sum is σ = 21122640. Its totient is φ = 21091876.

The previous prime is 21107243. The next prime is 21107267. The reversal of 21107257 is 75270112.

It is a happy number.

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 21107257 - 2¹⁵ = 21074489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21107227) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5407 + ... + 8452.

It is an arithmetic number, because the mean of its divisors is an integer number (5280660).

Almost surely, 2^21107257 is an apocalyptic number.

It is an amenable number.

21107257 is a deficient number, since it is larger than the sum of its proper divisors (15383).

21107257 is a wasteful number, since it uses less digits than its factorization.

21107257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15382.

The product of its (nonzero) digits is 980, while the sum is 25.

The square root of 21107257 is about 4594.2634883080. The cubic root of 21107257 is about 276.3613248824.

Adding to 21107257 its reverse (75270112), we get a palindrome (96377369).

The spelling of 21107257 in words is "twenty-one million, one hundred seven thousand, two hundred fifty-seven".