21366564 has 48 divisors (see below), whose sum is σ = 54190080. Its totient is φ = 6527520.

The previous prime is 21366557. The next prime is 21366581. The reversal of 21366564 is 46566312.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5557 + ... + 8579.

It is an arithmetic number, because the mean of its divisors is an integer number (1128960).

Almost surely, 2^21366564 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21366564, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27095040).

21366564 is an abundant number, since it is smaller than the sum of its proper divisors (32823516).

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

21366564 is a wasteful number, since it uses less digits than its factorization.

21366564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3080 (or 3078 counting only the distinct ones).

The product of its digits is 25920, while the sum is 33.

The square root of 21366564 is about 4622.3980789196. The cubic root of 21366564 is about 277.4884403918.

The spelling of 21366564 in words is "twenty-one million, three hundred sixty-six thousand, five hundred sixty-four".