21206563 has 12 divisors (see below), whose sum is σ = 24775392. Its totient is φ = 18098640.

The previous prime is 21206561. The next prime is 21206579. The reversal of 21206563 is 36560212.

It is not a de Polignac number, because 21206563 - 2¹ = 21206561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21206561) 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 11 ways as a sum of consecutive naturals, for example, 12481 + ... + 14077.

It is an arithmetic number, because the mean of its divisors is an integer number (2064616).

Almost surely, 2^21206563 is an apocalyptic number.

21206563 is a deficient number, since it is larger than the sum of its proper divisors (3568829).

21206563 is a wasteful number, since it uses less digits than its factorization.

21206563 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1882 (or 1875 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 25.

The square root of 21206563 is about 4605.0584143961. The cubic root of 21206563 is about 276.7940577191.

Adding to 21206563 its reverse (36560212), we get a palindrome (57766775).

The spelling of 21206563 in words is "twenty-one million, two hundred six thousand, five hundred sixty-three".