21043931 has 4 divisors (see below), whose sum is σ = 21126072. Its totient is φ = 20961792.

The previous prime is 21043927. The next prime is 21043949. The reversal of 21043931 is 13934012.

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 21043931 - 2² = 21043927 is a prime.

It is a super-2 number, since 2×21043931² = 885694063865522, 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 = 21043897 and 21043906.

It is not an unprimeable number, because it can be changed into a prime (21043901) 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, 40685 + ... + 41198.

It is an arithmetic number, because the mean of its divisors is an integer number (5281518).

Almost surely, 2^21043931 is an apocalyptic number.

21043931 is a deficient number, since it is larger than the sum of its proper divisors (82141).

21043931 is an equidigital number, since it uses as much as digits as its factorization.

21043931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82140.

The product of its (nonzero) digits is 648, while the sum is 23.

The square root of 21043931 is about 4587.3664558219. The cubic root of 21043931 is about 276.0846682407.

Adding to 21043931 its reverse (13934012), we get a palindrome (34977943).

The spelling of 21043931 in words is "twenty-one million, forty-three thousand, nine hundred thirty-one".