21042031 has 4 divisors (see below), whose sum is σ = 21330352. Its totient is φ = 20753712.

The previous prime is 21042017. The next prime is 21042053. The reversal of 21042031 is 13024012.

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

It is a cyclic number.

It is not a de Polignac number, because 21042031 - 2⁹ = 21041519 is a prime.

It is a super-2 number, since 2×21042031² = 885534137209922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042731) 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, 144051 + ... + 144196.

It is an arithmetic number, because the mean of its divisors is an integer number (5332588).

Almost surely, 2^21042031 is an apocalyptic number.

21042031 is a deficient number, since it is larger than the sum of its proper divisors (288321).

21042031 is an equidigital number, since it uses as much as digits as its factorization.

21042031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 288320.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21042031 is about 4587.1593606501. The cubic root of 21042031 is about 276.0763590096.

Adding to 21042031 its reverse (13024012), we get a palindrome (34066043).

The spelling of 21042031 in words is "twenty-one million, forty-two thousand, thirty-one".