999856021 has 2 divisors, whose sum is σ = 999856022. Its totient is φ = 999856020.

The previous prime is 999855991. The next prime is 999856031. The reversal of 999856021 is 120658999.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 932386225 + 67469796 = 30535^2 + 8214^2 .

It is a cyclic number.

It is not a de Polignac number, because 999856021 - 2⁷ = 999855893 is a prime.

It is the 31621-st Hogben number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999856031) by changing a digit.

It is a nontrivial repunit in base 31620.

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, 499928010 + 499928011.

It is an arithmetic number, because the mean of its divisors is an integer number (499928011).

Almost surely, 2^999856021 is an apocalyptic number.

It is an amenable number.

999856021 is a deficient number, since it is larger than the sum of its proper divisors (1).

999856021 is an equidigital number, since it uses as much as digits as its factorization.

999856021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 349920, while the sum is 49.

The square root of 999856021 is about 31620.5000118594. The cubic root of 999856021 is about 999.9520046965.

The spelling of 999856021 in words is "nine hundred ninety-nine million, eight hundred fifty-six thousand, twenty-one".