21153231 has 20 divisors (see below), whose sum is σ = 34473384. Its totient is φ = 12819600.

The previous prime is 21153227. The next prime is 21153257. The reversal of 21153231 is 13235112.

It is not a de Polignac number, because 21153231 - 2² = 21153227 is a prime.

It is a super-2 number, since 2×21153231² = 894918363478722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21153281) 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 19 ways as a sum of consecutive naturals, for example, 10980 + ... + 12761.

Almost surely, 2^21153231 is an apocalyptic number.

21153231 is a deficient number, since it is larger than the sum of its proper divisors (13320153).

21153231 is a wasteful number, since it uses less digits than its factorization.

21153231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23764 (or 23755 counting only the distinct ones).

The product of its digits is 180, while the sum is 18.

The square root of 21153231 is about 4599.2641802793. The cubic root of 21153231 is about 276.5618281512.

Adding to 21153231 its reverse (13235112), we get a palindrome (34388343).

The spelling of 21153231 in words is "twenty-one million, one hundred fifty-three thousand, two hundred thirty-one".