21520723 has 4 divisors (see below), whose sum is σ = 24595120. Its totient is φ = 18446328.

The previous prime is 21520721. The next prime is 21520729. The reversal of 21520723 is 32702512.

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 21520723 - 2¹ = 21520721 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21520694 and 21520703.

It is not an unprimeable number, because it can be changed into a prime (21520721) 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, 1537188 + ... + 1537201.

It is an arithmetic number, because the mean of its divisors is an integer number (6148780).

Almost surely, 2^21520723 is an apocalyptic number.

21520723 is a deficient number, since it is larger than the sum of its proper divisors (3074397).

21520723 is an equidigital number, since it uses as much as digits as its factorization.

21520723 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3074396.

The product of its (nonzero) digits is 840, while the sum is 22.

The square root of 21520723 is about 4639.0433281012. The cubic root of 21520723 is about 278.1541982223.

The spelling of 21520723 in words is "twenty-one million, five hundred twenty thousand, seven hundred twenty-three".