21813231 has 16 divisors (see below), whose sum is σ = 31840128. Its totient is φ = 13173600.

The previous prime is 21813179. The next prime is 21813247. The reversal of 21813231 is 13231812.

It is not a de Polignac number, because 21813231 - 2¹⁵ = 21780463 is a prime.

It is a super-2 number, since 2×21813231² = 951634093318722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21813198 and 21813207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21813251) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9925 + ... + 11921.

It is an arithmetic number, because the mean of its divisors is an integer number (1990008).

Almost surely, 2^21813231 is an apocalyptic number.

21813231 is a deficient number, since it is larger than the sum of its proper divisors (10026897).

21813231 is a wasteful number, since it uses less digits than its factorization.

21813231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2342.

The product of its digits is 288, while the sum is 21.

The square root of 21813231 is about 4670.4636814775. The cubic root of 21813231 is about 279.4087481315.

The spelling of 21813231 in words is "twenty-one million, eight hundred thirteen thousand, two hundred thirty-one".