990001 has 2 divisors, whose sum is σ = 990002. Its totient is φ = 990000.

The previous prime is 989999. The next prime is 990013. The reversal of 990001 is 100099.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 600625 + 389376 = 775^2 + 624^2 .

It is a cyclic number.

It is not a de Polignac number, because 990001 - 2¹ = 989999 is a prime.

Together with 989999, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (993001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495000 + 495001.

It is an arithmetic number, because the mean of its divisors is an integer number (495001).

2⁹⁹⁰⁰⁰¹ is an apocalyptic number.

It is an amenable number.

990001 is a deficient number, since it is larger than the sum of its proper divisors (1).

990001 is an equidigital number, since it uses as much as digits as its factorization.

990001 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 81, while the sum is 19.

The square root of 990001 is about 994.9879396254. The cubic root of 990001 is about 99.6655828987.

The spelling of 990001 in words is "nine hundred ninety thousand, one".