999021 has 8 divisors (see below), whose sum is σ = 1378080. Its totient is φ = 642992.

The previous prime is 999007. The next prime is 999023. The reversal of 999021 is 120999.

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

It is a cyclic number.

It is not a de Polignac number, because 999021 - 2⁵ = 998989 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 999021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (999023) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5655 + ... + 5828.

It is an arithmetic number, because the mean of its divisors is an integer number (172260).

2⁹⁹⁹⁰²¹ is an apocalyptic number.

It is an amenable number.

999021 is a deficient number, since it is larger than the sum of its proper divisors (379059).

999021 is a wasteful number, since it uses less digits than its factorization.

999021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11515.

The product of its (nonzero) digits is 1458, while the sum is 30.

The square root of 999021 is about 999.5103801362. The cubic root of 999021 is about 99.9673560115.

Subtracting from 999021 its sum of digits (30), we obtain a triangular number (998991 = T₁₄₁₃).

It can be divided in two parts, 9990 and 21, that added together give a triangular number (10011 = T₁₄₁).

The spelling of 999021 in words is "nine hundred ninety-nine thousand, twenty-one".