21043537 has 4 divisors (see below), whose sum is σ = 21556836. Its totient is φ = 20530240.

The previous prime is 21043523. The next prime is 21043543. The reversal of 21043537 is 73534012.

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 5035536 + 16008001 = 2244^2 + 4001^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043537 - 2⁷ = 21043409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21043567) 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, 256588 + ... + 256669.

It is an arithmetic number, because the mean of its divisors is an integer number (5389209).

Almost surely, 2^21043537 is an apocalyptic number.

It is an amenable number.

21043537 is a deficient number, since it is larger than the sum of its proper divisors (513299).

21043537 is an equidigital number, since it uses as much as digits as its factorization.

21043537 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 513298.

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

The square root of 21043537 is about 4587.3235115915. The cubic root of 21043537 is about 276.0829452096.

Adding to 21043537 its reverse (73534012), we get a palindrome (94577549).

The spelling of 21043537 in words is "twenty-one million, forty-three thousand, five hundred thirty-seven".