21055566 has 64 divisors (see below), whose sum is σ = 50803200. Its totient is φ = 5690496.

The previous prime is 21055561. The next prime is 21055579. The reversal of 21055566 is 66555012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21055561) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 71716 + ... + 72008.

It is an arithmetic number, because the mean of its divisors is an integer number (793800).

Almost surely, 2^21055566 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21055566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25401600).

21055566 is an abundant number, since it is smaller than the sum of its proper divisors (29747634).

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

21055566 is a wasteful number, since it uses less digits than its factorization.

21055566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 393.

The product of its (nonzero) digits is 9000, while the sum is 30.

The square root of 21055566 is about 4588.6344373898. The cubic root of 21055566 is about 276.1355404421.

The spelling of 21055566 in words is "twenty-one million, fifty-five thousand, five hundred sixty-six".