990021 has 8 divisors (see below), whose sum is σ = 1325344. Its totient is φ = 657360.

The previous prime is 990013. The next prime is 990023. The reversal of 990021 is 120099.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 990021 - 2³ = 990013 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 990021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (990023) 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 in 7 ways as a sum of consecutive naturals, for example, 495 + ... + 1491.

It is an arithmetic number, because the mean of its divisors is an integer number (165668).

2⁹⁹⁰⁰²¹ is an apocalyptic number.

It is an amenable number.

990021 is a deficient number, since it is larger than the sum of its proper divisors (335323).

990021 is a wasteful number, since it uses less digits than its factorization.

990021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1331.

The product of its (nonzero) digits is 162, while the sum is 21.

The square root of 990021 is about 994.9979899477. The cubic root of 990021 is about 99.6662540422. Note that the first 3 decimals are identical.

The spelling of 990021 in words is "nine hundred ninety thousand, twenty-one".