21806831 has 2 divisors, whose sum is σ = 21806832. Its totient is φ = 21806830.

The previous prime is 21806819. The next prime is 21806843. The reversal of 21806831 is 13860812.

It is a balanced prime because it is at equal distance from previous prime (21806819) and next prime (21806843).

It is a cyclic number.

It is not a de Polignac number, because 21806831 - 2¹⁰ = 21805807 is a prime.

It is a super-2 number, since 2×21806831² = 951075756525122, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21806794 and 21806803.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21806881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10903415 + 10903416.

It is an arithmetic number, because the mean of its divisors is an integer number (10903416).

Almost surely, 2^21806831 is an apocalyptic number.

21806831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21806831 is an equidigital number, since it uses as much as digits as its factorization.

21806831 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 21806831 is about 4669.7784744033. The cubic root of 21806831 is about 279.3814192914.

The spelling of 21806831 in words is "twenty-one million, eight hundred six thousand, eight hundred thirty-one".