21129231 has 4 divisors (see below), whose sum is σ = 28172312. Its totient is φ = 14086152.

The previous prime is 21129221. The next prime is 21129239. The reversal of 21129231 is 13292112.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21129231 - 2⁶ = 21129167 is a prime.

It is a super-2 number, since 2×21129231² = 892888805302722, 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 = 21129198 and 21129207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21129239) 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, 3521536 + ... + 3521541.

It is an arithmetic number, because the mean of its divisors is an integer number (7043078).

Almost surely, 2^21129231 is an apocalyptic number.

21129231 is a deficient number, since it is larger than the sum of its proper divisors (7043081).

21129231 is an equidigital number, since it uses as much as digits as its factorization.

21129231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7043080.

The product of its digits is 216, while the sum is 21.

The square root of 21129231 is about 4596.6543267903. The cubic root of 21129231 is about 276.4571948731.

The spelling of 21129231 in words is "twenty-one million, one hundred twenty-nine thousand, two hundred thirty-one".