11931991 has 2 divisors, whose sum is σ = 11931992. Its totient is φ = 11931990.

The previous prime is 11931989. The next prime is 11932007. The reversal of 11931991 is 19913911.

11931991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is an emirp because it is prime and its reverse (19913911) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 11931991 - 2¹ = 11931989 is a prime.

Together with 11931989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11931901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5965995 + 5965996.

It is an arithmetic number, because the mean of its divisors is an integer number (5965996).

Almost surely, 2^11931991 is an apocalyptic number.

11931991 is a deficient number, since it is larger than the sum of its proper divisors (1).

11931991 is an equidigital number, since it uses as much as digits as its factorization.

11931991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2187, while the sum is 34.

The square root of 11931991 is about 3454.2714137717. The cubic root of 11931991 is about 228.5095240282.

The spelling of 11931991 in words is "eleven million, nine hundred thirty-one thousand, nine hundred ninety-one".