21563231 has 4 divisors (see below), whose sum is σ = 21573792. Its totient is φ = 21552672.

The previous prime is 21563219. The next prime is 21563237. The reversal of 21563231 is 13236512.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21563231 - 2¹⁸ = 21301087 is a prime.

It is a super-2 number, since 2×21563231² = 929945862318722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21563197 and 21563206.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21563237) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1130 + ... + 6663.

It is an arithmetic number, because the mean of its divisors is an integer number (5393448).

Almost surely, 2^21563231 is an apocalyptic number.

21563231 is a deficient number, since it is larger than the sum of its proper divisors (10561).

21563231 is an equidigital number, since it uses as much as digits as its factorization.

21563231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10560.

The product of its digits is 1080, while the sum is 23.

The square root of 21563231 is about 4643.6226160187. The cubic root of 21563231 is about 278.3372156542.

Adding to 21563231 its reverse (13236512), we get a palindrome (34799743).

The spelling of 21563231 in words is "twenty-one million, five hundred sixty-three thousand, two hundred thirty-one".