391008991 has 4 divisors (see below), whose sum is σ = 391115872. Its totient is φ = 390902112.

The previous prime is 391008979. The next prime is 391009013. The reversal of 391008991 is 199800193.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199800193 = 61 ⋅3275413.

It is a cyclic number.

It is not a de Polignac number, because 391008991 - 2¹⁷ = 390877919 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (391008911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47751 + ... + 55336.

It is an arithmetic number, because the mean of its divisors is an integer number (97778968).

Almost surely, 2^391008991 is an apocalyptic number.

391008991 is a deficient number, since it is larger than the sum of its proper divisors (106881).

391008991 is a wasteful number, since it uses less digits than its factorization.

391008991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 106880.

The product of its (nonzero) digits is 17496, while the sum is 40.

The square root of 391008991 is about 19773.9472791853. The cubic root of 391008991 is about 731.2438860277.

The spelling of 391008991 in words is "three hundred ninety-one million, eight thousand, nine hundred ninety-one".