1311999991 has 4 divisors (see below), whose sum is σ = 1357241400. Its totient is φ = 1266758584.

The previous prime is 1311999979. The next prime is 1312000003. The reversal of 1311999991 is 1999991131.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (1311999979) and next prime (1312000003).

It is a cyclic number.

It is not a de Polignac number, because 1311999991 - 2¹⁷ = 1311868919 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 (1311999901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22620661 + ... + 22620718.

It is an arithmetic number, because the mean of its divisors is an integer number (339310350).

Almost surely, 2^1311999991 is an apocalyptic number.

1311999991 is a deficient number, since it is larger than the sum of its proper divisors (45241409).

1311999991 is an equidigital number, since it uses as much as digits as its factorization.

1311999991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45241408.

The product of its digits is 177147, while the sum is 52.

The square root of 1311999991 is about 36221.5404283142. The cubic root of 1311999991 is about 1094.7407324565.

The spelling of 1311999991 in words is "one billion, three hundred eleven million, nine hundred ninety-nine thousand, nine hundred ninety-one".