21205564 has 6 divisors (see below), whose sum is σ = 37109744. Its totient is φ = 10602780.

The previous prime is 21205559. The next prime is 21205573. The reversal of 21205564 is 46550212.

It is a congruent number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 2650692 + ... + 2650699.

Almost surely, 2^21205564 is an apocalyptic number.

It is an amenable number.

21205564 is a deficient number, since it is larger than the sum of its proper divisors (15904180).

21205564 is a wasteful number, since it uses less digits than its factorization.

21205564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5301395 (or 5301393 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 25.

The square root of 21205564 is about 4604.9499454391. The cubic root of 21205564 is about 276.7897112406.

Adding to 21205564 its reverse (46550212), we get a palindrome (67755776).

The spelling of 21205564 in words is "twenty-one million, two hundred five thousand, five hundred sixty-four".