81078991 has 4 divisors (see below), whose sum is σ = 92661712. Its totient is φ = 69496272.

The previous prime is 81078989. The next prime is 81079013. The reversal of 81078991 is 19987018.

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

It is a cyclic number.

It is not a de Polignac number, because 81078991 - 2¹ = 81078989 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 (81078961) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5791350 + ... + 5791363.

It is an arithmetic number, because the mean of its divisors is an integer number (23165428).

Almost surely, 2^81078991 is an apocalyptic number.

81078991 is a deficient number, since it is larger than the sum of its proper divisors (11582721).

81078991 is a wasteful number, since it uses less digits than its factorization.

81078991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11582720.

The product of its (nonzero) digits is 36288, while the sum is 43.

The square root of 81078991 is about 9004.3873195237. The cubic root of 81078991 is about 432.8154732192.

The spelling of 81078991 in words is "eighty-one million, seventy-eight thousand, nine hundred ninety-one".