391978 has 8 divisors (see below), whose sum is σ = 603972. Its totient is φ = 190656.

The previous prime is 391967. The next prime is 391987. The reversal of 391978 is 879193.

It can be written as a sum of positive squares in 2 ways, for example, as 332929 + 59049 = 577^2 + 243^2 .

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

It is a Harshad number since it is a multiple of its sum of digits (37).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2575 + ... + 2722.

2³⁹¹⁹⁷⁸ is an apocalyptic number.

391978 is a deficient number, since it is larger than the sum of its proper divisors (211994).

391978 is a wasteful number, since it uses less digits than its factorization.

391978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5336.

The product of its digits is 13608, while the sum is 37.

The square root of 391978 is about 626.0814643479. The cubic root of 391978 is about 73.1847450469.

It can be divided in two parts, 391 and 978, that added together give a square (1369 = 37²).

The spelling of 391978 in words is "three hundred ninety-one thousand, nine hundred seventy-eight".