391681987 has 2 divisors, whose sum is σ = 391681988. Its totient is φ = 391681986.

The previous prime is 391681919. The next prime is 391682099. The reversal of 391681987 is 789186193.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 391681987 - 2¹⁹ = 391157699 is a prime.

It is not a weakly prime, because it can be changed into another prime (391681687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195840993 + 195840994.

It is an arithmetic number, because the mean of its divisors is an integer number (195840994).

Almost surely, 2^391681987 is an apocalyptic number.

391681987 is a deficient number, since it is larger than the sum of its proper divisors (1).

391681987 is an equidigital number, since it uses as much as digits as its factorization.

391681987 is an evil number, because the sum of its binary digits is even.

The product of its digits is 653184, while the sum is 52.

The square root of 391681987 is about 19790.9572027227. The cubic root of 391681987 is about 731.6631791445.

The spelling of 391681987 in words is "three hundred ninety-one million, six hundred eighty-one thousand, nine hundred eighty-seven".