21006564 has 24 divisors (see below), whose sum is σ = 49095648. Its totient is φ = 6990720.

The previous prime is 21006563. The next prime is 21006593. The reversal of 21006564 is 46560012.

It is not an unprimeable number, because it can be changed into a prime (21006563) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9579 + ... + 11565.

It is an arithmetic number, because the mean of its divisors is an integer number (2045652).

Almost surely, 2^21006564 is an apocalyptic number.

It is an amenable number.

21006564 is an abundant number, since it is smaller than the sum of its proper divisors (28089084).

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

21006564 is a wasteful number, since it uses less digits than its factorization.

21006564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2875 (or 2873 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21006564 is about 4583.2918301151. The cubic root of 21006564 is about 275.9211600060.

Adding to 21006564 its reverse (46560012), we get a palindrome (67566576).

The spelling of 21006564 in words is "twenty-one million, six thousand, five hundred sixty-four".