1311021991 has 2 divisors, whose sum is σ = 1311021992. Its totient is φ = 1311021990.

The previous prime is 1311021979. The next prime is 1311022033. The reversal of 1311021991 is 1991201131.

It is a weak prime.

It is an emirp because it is prime and its reverse (1991201131) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1311021991 - 2⁹ = 1311021479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1311021941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 655510995 + 655510996.

It is an arithmetic number, because the mean of its divisors is an integer number (655510996).

Almost surely, 2^1311021991 is an apocalyptic number.

1311021991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1311021991 is an equidigital number, since it uses as much as digits as its factorization.

1311021991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 486, while the sum is 28.

The square root of 1311021991 is about 36208.0376574042. The cubic root of 1311021991 is about 1094.4686484661.

The spelling of 1311021991 in words is "one billion, three hundred eleven million, twenty-one thousand, nine hundred ninety-one".