399978 has 24 divisors (see below), whose sum is σ = 899808. Its totient is φ = 133164.

The previous prime is 399953. The next prime is 399979. The reversal of 399978 is 879993.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (399979) by changing a digit.

399978 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 75 + ... + 897.

It is an arithmetic number, because the mean of its divisors is an integer number (37492).

2³⁹⁹⁹⁷⁸ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 399978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (449904).

399978 is an abundant number, since it is smaller than the sum of its proper divisors (499830).

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

399978 is an equidigital number, since it uses as much as digits as its factorization.

399978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 840 (or 828 counting only the distinct ones).

The product of its digits is 122472, while the sum is 45.

The square root of 399978 is about 632.4381392674. The cubic root of 399978 is about 73.6792791365.

The spelling of 399978 in words is "three hundred ninety-nine thousand, nine hundred seventy-eight".