11531611991 has 2 divisors, whose sum is σ = 11531611992. Its totient is φ = 11531611990.

The previous prime is 11531611979. The next prime is 11531612003. The reversal of 11531611991 is 19911613511.

It is a balanced prime because it is at equal distance from previous prime (11531611979) and next prime (11531612003).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-11531611991 is a prime.

It is a super-2 number, since 2×11531611991² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11531619991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5765805995 + 5765805996.

It is an arithmetic number, because the mean of its divisors is an integer number (5765805996).

Almost surely, 2^11531611991 is an apocalyptic number.

11531611991 is a deficient number, since it is larger than the sum of its proper divisors (1).

11531611991 is an equidigital number, since it uses as much as digits as its factorization.

11531611991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7290, while the sum is 38.

The spelling of 11531611991 in words is "eleven billion, five hundred thirty-one million, six hundred eleven thousand, nine hundred ninety-one".