691978 has 24 divisors (see below), whose sum is σ = 1264032. Its totient is φ = 282744.

The previous prime is 691973. The next prime is 691979. The reversal of 691978 is 879196.

It is a self number, because there is not a number n which added to its sum of digits gives 691978.

It is not an unprimeable number, because it can be changed into a prime (691973) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2101 + ... + 2407.

It is an arithmetic number, because the mean of its divisors is an integer number (52668).

2⁶⁹¹⁹⁷⁸ is an apocalyptic number.

691978 is a deficient number, since it is larger than the sum of its proper divisors (572054).

691978 is a wasteful number, since it uses less digits than its factorization.

691978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 346 (or 339 counting only the distinct ones).

The product of its digits is 27216, while the sum is 40.

The square root of 691978 is about 831.8521503248. The cubic root of 691978 is about 88.4499168679.

The spelling of 691978 in words is "six hundred ninety-one thousand, nine hundred seventy-eight".