21056831 has 2 divisors, whose sum is σ = 21056832. Its totient is φ = 21056830.

The previous prime is 21056801. The next prime is 21056839. The reversal of 21056831 is 13865012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21056831 - 2¹⁰ = 21055807 is a prime.

It is a super-2 number, since 2×21056831² = 886780263525122, which contains 22 as substring.

It is a Chen prime.

It is equal to p_1333358 and since 21056831 and 1333358 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21056831.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21056839) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10528415 + 10528416.

It is an arithmetic number, because the mean of its divisors is an integer number (10528416).

Almost surely, 2^21056831 is an apocalyptic number.

21056831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21056831 is an equidigital number, since it uses as much as digits as its factorization.

21056831 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1440, while the sum is 26.

The square root of 21056831 is about 4588.7722758925. The cubic root of 21056831 is about 276.1410703253.

Subtracting from 21056831 its sum of digits (26), we obtain a triangular number (21056805 = T₆₄₈₉).

The spelling of 21056831 in words is "twenty-one million, fifty-six thousand, eight hundred thirty-one".