390991 has 2 divisors, whose sum is σ = 390992. Its totient is φ = 390990.

The previous prime is 390989. The next prime is 391009. The reversal of 390991 is 199093.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 390991 - 2¹ = 390989 is a prime.

Together with 390989, it forms a pair of twin primes.

390991 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (390961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195495 + 195496.

It is an arithmetic number, because the mean of its divisors is an integer number (195496).

2³⁹⁰⁹⁹¹ is an apocalyptic number.

390991 is a deficient number, since it is larger than the sum of its proper divisors (1).

390991 is an equidigital number, since it uses as much as digits as its factorization.

390991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2187, while the sum is 31.

The square root of 390991 is about 625.2927314466. The cubic root of 390991 is about 73.1232670590.

The spelling of 390991 in words is "three hundred ninety thousand, nine hundred ninety-one".