999867821 has 2 divisors, whose sum is σ = 999867822. Its totient is φ = 999867820.

The previous prime is 999867811. The next prime is 999867823. The reversal of 999867821 is 128768999.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 754600900 + 245266921 = 27470^2 + 15661^2 .

It is a cyclic number.

It is not a de Polignac number, because 999867821 - 2¹⁰ = 999866797 is a prime.

Together with 999867823, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999867823) by changing a digit.

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

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499933910 + 499933911.

It is an arithmetic number, because the mean of its divisors is an integer number (499933911).

Almost surely, 2^999867821 is an apocalyptic number.

It is an amenable number.

999867821 is a deficient number, since it is larger than the sum of its proper divisors (1).

999867821 is an equidigital number, since it uses as much as digits as its factorization.

999867821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3919104, while the sum is 59.

The square root of 999867821 is about 31620.6865991237. The cubic root of 999867821 is about 999.9559383919.

The spelling of 999867821 in words is "nine hundred ninety-nine million, eight hundred sixty-seven thousand, eight hundred twenty-one".