399691 has 2 divisors, whose sum is σ = 399692. Its totient is φ = 399690.

The previous prime is 399689. The next prime is 399719. The reversal of 399691 is 196993.

It is a weak prime.

It is an emirp because it is prime and its reverse (196993) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 399691 - 2¹ = 399689 is a prime.

Together with 399689, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 399691.

It is not a weakly prime, because it can be changed into another prime (399601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 199845 + 199846.

It is an arithmetic number, because the mean of its divisors is an integer number (199846).

2³⁹⁹⁶⁹¹ is an apocalyptic number.

399691 is a deficient number, since it is larger than the sum of its proper divisors (1).

399691 is an equidigital number, since it uses as much as digits as its factorization.

399691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13122, while the sum is 37.

The square root of 399691 is about 632.2111988885. The cubic root of 399691 is about 73.6616523230.

It can be divided in two parts, 39 and 9691, that added together give a triangular number (9730 = T₁₃₉).

The spelling of 399691 in words is "three hundred ninety-nine thousand, six hundred ninety-one".