21289231 has 4 divisors (see below), whose sum is σ = 21298464. Its totient is φ = 21280000.

The previous prime is 21289211. The next prime is 21289249. The reversal of 21289231 is 13298212.

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 21289231 - 2¹⁹ = 20764943 is a prime.

It is a super-2 number, since 2×21289231² = 906462713142722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21289231.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21289201) 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, 2106 + ... + 6856.

It is an arithmetic number, because the mean of its divisors is an integer number (5324616).

Almost surely, 2^21289231 is an apocalyptic number.

21289231 is a deficient number, since it is larger than the sum of its proper divisors (9233).

21289231 is an equidigital number, since it uses as much as digits as its factorization.

21289231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9232.

The product of its digits is 1728, while the sum is 28.

The square root of 21289231 is about 4614.0254659028. The cubic root of 21289231 is about 277.1532600769.

The spelling of 21289231 in words is "twenty-one million, two hundred eighty-nine thousand, two hundred thirty-one".