21042564 has 12 divisors (see below), whose sum is σ = 49099344. Its totient is φ = 7014184.

The previous prime is 21042563. The next prime is 21042577. The reversal of 21042564 is 46524012.

It is a tau number, because it is divible by the number of its divisors (12).

It is not an unprimeable number, because it can be changed into a prime (21042563) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 876762 + ... + 876785.

It is an arithmetic number, because the mean of its divisors is an integer number (4091612).

Almost surely, 2^21042564 is an apocalyptic number.

It is an amenable number.

21042564 is an abundant number, since it is smaller than the sum of its proper divisors (28056780).

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

21042564 is a wasteful number, since it uses less digits than its factorization.

21042564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1753554 (or 1753552 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21042564 is about 4587.2174572392. The cubic root of 21042564 is about 276.0786900180.

Adding to 21042564 its reverse (46524012), we get a palindrome (67566576).

The spelling of 21042564 in words is "twenty-one million, forty-two thousand, five hundred sixty-four".