21993820 has 24 divisors (see below), whose sum is σ = 46275264. Its totient is φ = 8780736.

The previous prime is 21993809. The next prime is 21993823. The reversal of 21993820 is 2839912.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21993823) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19389 + ... + 20491.

It is an arithmetic number, because the mean of its divisors is an integer number (1928136).

Almost surely, 2^21993820 is an apocalyptic number.

21993820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21993820 is an abundant number, since it is smaller than the sum of its proper divisors (24281444).

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

21993820 is a wasteful number, since it uses less digits than its factorization.

21993820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2109 (or 2107 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 34.

The square root of 21993820 is about 4689.7569233384. The cubic root of 21993820 is about 280.1776933310.

The spelling of 21993820 in words is "twenty-one million, nine hundred ninety-three thousand, eight hundred twenty".