21523157 has 4 divisors (see below), whose sum is σ = 21724416. Its totient is φ = 21321900.

The previous prime is 21523093. The next prime is 21523171. The reversal of 21523157 is 75132512.

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 21523157 - 2⁶ = 21523093 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 (21553157) 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, 100469 + ... + 100682.

It is an arithmetic number, because the mean of its divisors is an integer number (5431104).

Almost surely, 2^21523157 is an apocalyptic number.

It is an amenable number.

21523157 is a deficient number, since it is larger than the sum of its proper divisors (201259).

21523157 is a wasteful number, since it uses less digits than its factorization.

21523157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201258.

The product of its digits is 2100, while the sum is 26.

The square root of 21523157 is about 4639.3056592555. The cubic root of 21523157 is about 278.1646842671.

Adding to 21523157 its reverse (75132512), we get a palindrome (96655669).

The spelling of 21523157 in words is "twenty-one million, five hundred twenty-three thousand, one hundred fifty-seven".