391987 has 2 divisors, whose sum is σ = 391988. Its totient is φ = 391986.

The previous prime is 391967. The next prime is 391999. The reversal of 391987 is 789193.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-391987 is a prime.

It is not a weakly prime, because it can be changed into another prime (391907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195993 + 195994.

It is an arithmetic number, because the mean of its divisors is an integer number (195994).

2³⁹¹⁹⁸⁷ is an apocalyptic number.

391987 is a deficient number, since it is larger than the sum of its proper divisors (1).

391987 is an equidigital number, since it uses as much as digits as its factorization.

391987 is an odious number, because the sum of its binary digits is odd.

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

The square root of 391987 is about 626.0886518697. The cubic root of 391987 is about 73.1853051613.

It can be divided in two parts, 391 and 987, that added together give a triangular number (1378 = T₅₂).

The spelling of 391987 in words is "three hundred ninety-one thousand, nine hundred eighty-seven".