21004031 has 6 divisors (see below), whose sum is σ = 21326760. Its totient is φ = 20686116.

The previous prime is 21003937. The next prime is 21004043. The reversal of 21004031 is 13040012.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-21004031 is a prime.

It is a super-2 number, since 2×21004031² = 882338636497922, 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 (21004331) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2150 + ... + 6828.

It is an arithmetic number, because the mean of its divisors is an integer number (3554460).

Almost surely, 2^21004031 is an apocalyptic number.

21004031 is a deficient number, since it is larger than the sum of its proper divisors (322729).

21004031 is an frugal number, since it uses more digits than its factorization.

21004031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4813 (or 4746 counting only the distinct ones).

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21004031 is about 4583.0154920096. The cubic root of 21004031 is about 275.9100692442.

Adding to 21004031 its reverse (13040012), we get a palindrome (34044043).

The spelling of 21004031 in words is "twenty-one million, four thousand, thirty-one".