21523723 has 4 divisors (see below), whose sum is σ = 23179408. Its totient is φ = 19868040.

The previous prime is 21523681. The next prime is 21523727. The reversal of 21523723 is 32732512.

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

It is a cyclic number.

It is not a de Polignac number, because 21523723 - 2²¹ = 19426571 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21523727) 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, 827823 + ... + 827848.

It is an arithmetic number, because the mean of its divisors is an integer number (5794852).

Almost surely, 2^21523723 is an apocalyptic number.

21523723 is a deficient number, since it is larger than the sum of its proper divisors (1655685).

21523723 is a wasteful number, since it uses less digits than its factorization.

21523723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1655684.

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

The square root of 21523723 is about 4639.3666593620. The cubic root of 21523723 is about 278.1671225685.

The spelling of 21523723 in words is "twenty-one million, five hundred twenty-three thousand, seven hundred twenty-three".