81540991 has 4 divisors (see below), whose sum is σ = 93189712. Its totient is φ = 69892272.

The previous prime is 81540983. The next prime is 81541001. The reversal of 81540991 is 19904518.

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 81540991 - 2³ = 81540983 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81540991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81540961) 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, 5824350 + ... + 5824363.

It is an arithmetic number, because the mean of its divisors is an integer number (23297428).

Almost surely, 2^81540991 is an apocalyptic number.

81540991 is a deficient number, since it is larger than the sum of its proper divisors (11648721).

81540991 is a wasteful number, since it uses less digits than its factorization.

81540991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11648720.

The product of its (nonzero) digits is 12960, while the sum is 37.

The square root of 81540991 is about 9030.0050387583. The cubic root of 81540991 is about 433.6359987422.

The spelling of 81540991 in words is "eighty-one million, five hundred forty thousand, nine hundred ninety-one".