21866820 has 24 divisors (see below), whose sum is σ = 61227264. Its totient is φ = 5831136.

The previous prime is 21866809. The next prime is 21866821. The reversal of 21866820 is 2866812.

It is not an unprimeable number, because it can be changed into a prime (21866821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 182164 + ... + 182283.

It is an arithmetic number, because the mean of its divisors is an integer number (2551136).

Almost surely, 2^21866820 is an apocalyptic number.

21866820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21866820 is an abundant number, since it is smaller than the sum of its proper divisors (39360444).

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

21866820 is a wasteful number, since it uses less digits than its factorization.

21866820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 364459 (or 364457 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 33.

The square root of 21866820 is about 4676.1971729173. The cubic root of 21866820 is about 279.6373706959.

The spelling of 21866820 in words is "twenty-one million, eight hundred sixty-six thousand, eight hundred twenty".