81191191 has 2 divisors, whose sum is σ = 81191192. Its totient is φ = 81191190.

The previous prime is 81191147. The next prime is 81191197. The reversal of 81191191 is 19119118.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81191191 - 2²⁵ = 47636759 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81191197) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40595595 + 40595596.

It is an arithmetic number, because the mean of its divisors is an integer number (40595596).

Almost surely, 2^81191191 is an apocalyptic number.

81191191 is a deficient number, since it is larger than the sum of its proper divisors (1).

81191191 is an equidigital number, since it uses as much as digits as its factorization.

81191191 is an evil number, because the sum of its binary digits is even.

The product of its digits is 648, while the sum is 31.

The square root of 81191191 is about 9010.6154617762. The cubic root of 81191191 is about 433.0150296934.

The spelling of 81191191 in words is "eighty-one million, one hundred ninety-one thousand, one hundred ninety-one".