391261991 has 4 divisors (see below), whose sum is σ = 397676184. Its totient is φ = 384847800.

The previous prime is 391261979. The next prime is 391262009. The reversal of 391261991 is 199162193.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199162193 = 157 ⋅1268549.

It is a cyclic number.

It is not a de Polignac number, because 391261991 - 2²² = 387067687 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 (391261951) 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, 3207005 + ... + 3207126.

It is an arithmetic number, because the mean of its divisors is an integer number (99419046).

Almost surely, 2^391261991 is an apocalyptic number.

391261991 is a deficient number, since it is larger than the sum of its proper divisors (6414193).

391261991 is an equidigital number, since it uses as much as digits as its factorization.

391261991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6414192.

The product of its digits is 26244, while the sum is 41.

The square root of 391261991 is about 19780.3435511115. The cubic root of 391261991 is about 731.4015676665.

The spelling of 391261991 in words is "three hundred ninety-one million, two hundred sixty-one thousand, nine hundred ninety-one".