21008820 has 48 divisors (see below), whose sum is σ = 67229568. Its totient is φ = 4801920.

The previous prime is 21008797. The next prime is 21008833. The reversal of 21008820 is 2880012.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24591 + ... + 25430.

It is an arithmetic number, because the mean of its divisors is an integer number (1400616).

Almost surely, 2^21008820 is an apocalyptic number.

21008820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21008820 is an abundant number, since it is smaller than the sum of its proper divisors (46220748).

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

21008820 is a wasteful number, since it uses less digits than its factorization.

21008820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50040 (or 50038 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 21.

The square root of 21008820 is about 4583.5379348272. The cubic root of 21008820 is about 275.9310371704.

Adding to 21008820 its reverse (2880012), we get a palindrome (23888832).

The spelling of 21008820 in words is "twenty-one million, eight thousand, eight hundred twenty".