999820121 has 2 divisors, whose sum is σ = 999820122. Its totient is φ = 999820120.

The previous prime is 999820069. The next prime is 999820123. The reversal of 999820121 is 121028999.

999820121 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 829152025 + 170668096 = 28795^2 + 13064^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-999820121 is a prime.

It is a Sophie Germain prime.

Together with 999820123, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (999820123) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499910060 + 499910061.

It is an arithmetic number, because the mean of its divisors is an integer number (499910061).

Almost surely, 2^999820121 is an apocalyptic number.

It is an amenable number.

999820121 is a deficient number, since it is larger than the sum of its proper divisors (1).

999820121 is an equidigital number, since it uses as much as digits as its factorization.

999820121 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 23328, while the sum is 41.

The square root of 999820121 is about 31619.9323370560. The cubic root of 999820121 is about 999.9400367378.

The spelling of 999820121 in words is "nine hundred ninety-nine million, eight hundred twenty thousand, one hundred twenty-one".