21523237 has 4 divisors (see below), whose sum is σ = 22048236. Its totient is φ = 20998240.

The previous prime is 21523171. The next prime is 21523261. The reversal of 21523237 is 73232512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1147041 + 20376196 = 1071^2 + 4514^2 .

It is a cyclic number.

It is not a de Polignac number, because 21523237 - 2²³ = 13134629 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 (21523267) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 262438 + ... + 262519.

It is an arithmetic number, because the mean of its divisors is an integer number (5512059).

Almost surely, 2^21523237 is an apocalyptic number.

It is an amenable number.

21523237 is a deficient number, since it is larger than the sum of its proper divisors (524999).

21523237 is an equidigital number, since it uses as much as digits as its factorization.

21523237 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 524998.

The product of its digits is 2520, while the sum is 25.

The square root of 21523237 is about 4639.3142812273. The cubic root of 21523237 is about 278.1650289059.

Adding to 21523237 its reverse (73232512), we get a palindrome (94755749).

The spelling of 21523237 in words is "twenty-one million, five hundred twenty-three thousand, two hundred thirty-seven".