21657397 has 4 divisors (see below), whose sum is σ = 22797280. Its totient is φ = 20517516.

The previous prime is 21657367. The next prime is 21657401. The reversal of 21657397 is 79375612.

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 21657397 - 2¹⁹ = 21133109 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 (21657367) 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, 569913 + ... + 569950.

It is an arithmetic number, because the mean of its divisors is an integer number (5699320).

Almost surely, 2^21657397 is an apocalyptic number.

It is an amenable number.

21657397 is a deficient number, since it is larger than the sum of its proper divisors (1139883).

21657397 is a wasteful number, since it uses less digits than its factorization.

21657397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1139882.

The product of its digits is 79380, while the sum is 40.

The square root of 21657397 is about 4653.7508528068. The cubic root of 21657397 is about 278.7417907990.

The spelling of 21657397 in words is "twenty-one million, six hundred fifty-seven thousand, three hundred ninety-seven".