21188820 has 24 divisors (see below), whose sum is σ = 59328864. Its totient is φ = 5650336.

The previous prime is 21188803. The next prime is 21188887. The reversal of 21188820 is 2888112.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 176514 + ... + 176633.

It is an arithmetic number, because the mean of its divisors is an integer number (2472036).

Almost surely, 2^21188820 is an apocalyptic number.

21188820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21188820 is an abundant number, since it is smaller than the sum of its proper divisors (38140044).

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

21188820 is a wasteful number, since it uses less digits than its factorization.

21188820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 353159 (or 353157 counting only the distinct ones).

The product of its (nonzero) digits is 2048, while the sum is 30.

The square root of 21188820 is about 4603.1315427652. The cubic root of 21188820 is about 276.7168406285.

The spelling of 21188820 in words is "twenty-one million, one hundred eighty-eight thousand, eight hundred twenty".