1311991 has 2 divisors, whose sum is σ = 1311992. Its totient is φ = 1311990.

The previous prime is 1311971. The next prime is 1312001. The reversal of 1311991 is 1991131.

It is a strong prime.

It is an emirp because it is prime and its reverse (1991131) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1311991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1311901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 655995 + 655996.

It is an arithmetic number, because the mean of its divisors is an integer number (655996).

2^1311991 is an apocalyptic number.

1311991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1311991 is an equidigital number, since it uses as much as digits as its factorization.

1311991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 243, while the sum is 25.

The square root of 1311991 is about 1145.4217563850. The cubic root of 1311991 is about 109.4738231736.

The spelling of 1311991 in words is "one million, three hundred eleven thousand, nine hundred ninety-one".