21537723 has 4 divisors (see below), whose sum is σ = 28716968. Its totient is φ = 14358480.

The previous prime is 21537689. The next prime is 21537743. The reversal of 21537723 is 32773512.

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

It is not a de Polignac number, because 21537723 - 2¹⁰ = 21536699 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21537743) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3589618 + ... + 3589623.

It is an arithmetic number, because the mean of its divisors is an integer number (7179242).

Almost surely, 2^21537723 is an apocalyptic number.

21537723 is a deficient number, since it is larger than the sum of its proper divisors (7179245).

21537723 is an equidigital number, since it uses as much as digits as its factorization.

21537723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7179244.

The product of its digits is 8820, while the sum is 30.

The square root of 21537723 is about 4640.8752407278. The cubic root of 21537723 is about 278.2274203102.

The spelling of 21537723 in words is "twenty-one million, five hundred thirty-seven thousand, seven hundred twenty-three".