999921 has 8 divisors (see below), whose sum is σ = 1435840. Its totient is φ = 615312.

The previous prime is 999917. The next prime is 999931. The reversal of 999921 is 129999.

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 999921 - 2² = 999917 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39), and also a Moran number because the ratio is a prime number: 25639 = 999921 / (9 + 9 + 9 + 9 + 2 + 1).

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a self number, because there is not a number n which added to its sum of digits gives 999921.

It is not an unprimeable number, because it can be changed into a prime (999931) 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, 12781 + ... + 12858.

It is an arithmetic number, because the mean of its divisors is an integer number (179480).

2⁹⁹⁹⁹²¹ is an apocalyptic number.

It is an amenable number.

999921 is a deficient number, since it is larger than the sum of its proper divisors (435919).

999921 is a wasteful number, since it uses less digits than its factorization.

999921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25655.

The product of its digits is 13122, while the sum is 39.

The square root of 999921 is about 999.9604992198. The cubic root of 999921 is about 99.9973665973.

The spelling of 999921 in words is "nine hundred ninety-nine thousand, nine hundred twenty-one".