21123931 has 4 divisors (see below), whose sum is σ = 21135664. Its totient is φ = 21112200.

The previous prime is 21123917. The next prime is 21123983. The reversal of 21123931 is 13932112.

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 21123931 - 2⁵ = 21123899 is a prime.

It is a super-2 number, since 2×21123931² = 892440921785522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21123901) 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, 2535 + ... + 6976.

It is an arithmetic number, because the mean of its divisors is an integer number (5283916).

Almost surely, 2^21123931 is an apocalyptic number.

21123931 is a deficient number, since it is larger than the sum of its proper divisors (11733).

21123931 is an equidigital number, since it uses as much as digits as its factorization.

21123931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11732.

The product of its digits is 324, while the sum is 22.

The square root of 21123931 is about 4596.0777843722. The cubic root of 21123931 is about 276.4340776780.

It can be divided in two parts, 211 and 23931, that added together give a palindrome (24142).

The spelling of 21123931 in words is "twenty-one million, one hundred twenty-three thousand, nine hundred thirty-one".