21200820 has 48 divisors (see below), whose sum is σ = 59660160. Its totient is φ = 5625216.

The previous prime is 21200801. The next prime is 21200821. The reversal of 21200820 is 2800212.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21200820.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21200821) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12969 + ... + 14511.

It is an arithmetic number, because the mean of its divisors is an integer number (1242920).

Almost surely, 2^21200820 is an apocalyptic number.

21200820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21200820 is an abundant number, since it is smaller than the sum of its proper divisors (38459340).

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

21200820 is a wasteful number, since it uses less digits than its factorization.

21200820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1784 (or 1782 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 15.

The square root of 21200820 is about 4604.4348187373. The cubic root of 21200820 is about 276.7690690431.

The spelling of 21200820 in words is "twenty-one million, two hundred thousand, eight hundred twenty".