21021564 has 24 divisors (see below), whose sum is σ = 49302400. Its totient is φ = 6971184.

The previous prime is 21021529. The next prime is 21021569. The reversal of 21021564 is 46512012.

It is a self number, because there is not a number n which added to its sum of digits gives 21021564.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021569) 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, 2014 + ... + 6789.

Almost surely, 2^21021564 is an apocalyptic number.

It is an amenable number.

21021564 is an abundant number, since it is smaller than the sum of its proper divisors (28280836).

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

21021564 is a wasteful number, since it uses less digits than its factorization.

21021564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9009 (or 9007 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21021564 is about 4584.9279165544. The cubic root of 21021564 is about 275.9868193664.

Adding to 21021564 its reverse (46512012), we get a palindrome (67533576).

The spelling of 21021564 in words is "twenty-one million, twenty-one thousand, five hundred sixty-four".