21072831 has 16 divisors (see below), whose sum is σ = 30406656. Its totient is φ = 12904416.

The previous prime is 21072827. The next prime is 21072833. The reversal of 21072831 is 13827012.

It is not a de Polignac number, because 21072831 - 2² = 21072827 is a prime.

It is a super-2 number, since 2×21072831² = 888128412709122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21072833) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7486 + ... + 9908.

It is an arithmetic number, because the mean of its divisors is an integer number (1900416).

Almost surely, 2^21072831 is an apocalyptic number.

21072831 is a deficient number, since it is larger than the sum of its proper divisors (9333825).

21072831 is a wasteful number, since it uses less digits than its factorization.

21072831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2662.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21072831 is about 4590.5153305484. The cubic root of 21072831 is about 276.2109944041.

Adding to 21072831 its reverse (13827012), we get a palindrome (34899843).

The spelling of 21072831 in words is "twenty-one million, seventy-two thousand, eight hundred thirty-one".