999978 has 32 divisors (see below), whose sum is σ = 2367360. Its totient is φ = 275520.

The previous prime is 999961. The next prime is 999979. The reversal of 999978 is 879999.

It is an Ulam number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 999978.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 999978.

It is not an unprimeable number, because it can be changed into a prime (999979) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 808 + ... + 1628.

It is an arithmetic number, because the mean of its divisors is an integer number (73980).

2⁹⁹⁹⁹⁷⁸ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 999978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1183680).

999978 is an abundant number, since it is smaller than the sum of its proper divisors (1367382).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

999978 is a wasteful number, since it uses less digits than its factorization.

999978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 862.

The product of its digits is 367416, while the sum is 51.

The square root of 999978 is about 999.9889999395. The cubic root of 999978 is about 99.9992666613. Note that the first 3 decimals are identical.

The spelling of 999978 in words is "nine hundred ninety-nine thousand, nine hundred seventy-eight".