81108991 has 2 divisors, whose sum is σ = 81108992. Its totient is φ = 81108990.

The previous prime is 81108983. The next prime is 81109001. The reversal of 81108991 is 19980118.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81108991 - 2³ = 81108983 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81108991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81108961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40554495 + 40554496.

It is an arithmetic number, because the mean of its divisors is an integer number (40554496).

Almost surely, 2^81108991 is an apocalyptic number.

81108991 is a deficient number, since it is larger than the sum of its proper divisors (1).

81108991 is an equidigital number, since it uses as much as digits as its factorization.

81108991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 37.

The square root of 81108991 is about 9006.0530200527. The cubic root of 81108991 is about 432.8688485877.

The spelling of 81108991 in words is "eighty-one million, one hundred eight thousand, nine hundred ninety-one".