21540564 has 72 divisors (see below), whose sum is σ = 58699368. Its totient is φ = 6635520.

The previous prime is 21540553. The next prime is 21540583. The reversal of 21540564 is 46504512.

It can be written as a sum of positive squares in 4 ways, for example, as 6656400 + 14884164 = 2580^2 + 3858^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 37044 + ... + 37620.

It is an arithmetic number, because the mean of its divisors is an integer number (815269).

Almost surely, 2^21540564 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 21540564, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29349684).

21540564 is an abundant number, since it is smaller than the sum of its proper divisors (37158804).

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

21540564 is a wasteful number, since it uses less digits than its factorization.

21540564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 665 (or 660 counting only the distinct ones).

The product of its (nonzero) digits is 4800, while the sum is 27.

The square root of 21540564 is about 4641.1813151395. The cubic root of 21540564 is about 278.2396532553.

The spelling of 21540564 in words is "twenty-one million, five hundred forty thousand, five hundred sixty-four".