21008920 has 32 divisors (see below), whose sum is σ = 47401200. Its totient is φ = 8380288.

The previous prime is 21008903. The next prime is 21008941. The reversal of 21008920 is 2980012.

It is a junction number, because it is equal to n+sod(n) for n = 21008891 and 21008900.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 25962 + ... + 26758.

Almost surely, 2^21008920 is an apocalyptic number.

21008920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21008920 is an abundant number, since it is smaller than the sum of its proper divisors (26392280).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21008920 is a wasteful number, since it uses less digits than its factorization.

21008920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1467 (or 1463 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21008920 is about 4583.5488434182. The cubic root of 21008920 is about 275.9314749716.

Adding to 21008920 its reverse (2980012), we get a palindrome (23988932).

The spelling of 21008920 in words is "twenty-one million, eight thousand, nine hundred twenty".