21008873 has 4 divisors (see below), whose sum is σ = 21076308. Its totient is φ = 20941440.

The previous prime is 21008857. The next prime is 21008879. The reversal of 21008873 is 37880012.

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 3636649 + 17372224 = 1907^2 + 4168^2 .

It is a cyclic number.

It is not a de Polignac number, because 21008873 - 2⁴ = 21008857 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21008879) 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, 33248 + ... + 33873.

It is an arithmetic number, because the mean of its divisors is an integer number (5269077).

Almost surely, 2^21008873 is an apocalyptic number.

It is an amenable number.

21008873 is a deficient number, since it is larger than the sum of its proper divisors (67435).

21008873 is an equidigital number, since it uses as much as digits as its factorization.

21008873 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67434.

The product of its (nonzero) digits is 2688, while the sum is 29.

The square root of 21008873 is about 4583.5437163836. The cubic root of 21008873 is about 275.9312692052.

Adding to 21008873 its reverse (37880012), we get a palindrome (58888885).

The spelling of 21008873 in words is "twenty-one million, eight thousand, eight hundred seventy-three".