21687573 has 4 divisors (see below), whose sum is σ = 28916768. Its totient is φ = 14458380.

The previous prime is 21687559. The next prime is 21687581. The reversal of 21687573 is 37578612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21687573 - 2⁵ = 21687541 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 (21687553) 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, 3614593 + ... + 3614598.

It is an arithmetic number, because the mean of its divisors is an integer number (7229192).

Almost surely, 2^21687573 is an apocalyptic number.

It is an amenable number.

21687573 is a deficient number, since it is larger than the sum of its proper divisors (7229195).

21687573 is an equidigital number, since it uses as much as digits as its factorization.

21687573 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7229194.

The product of its digits is 70560, while the sum is 39.

The square root of 21687573 is about 4656.9918402333. The cubic root of 21687573 is about 278.8711909097.

The spelling of 21687573 in words is "twenty-one million, six hundred eighty-seven thousand, five hundred seventy-three".