81538591 has 8 divisors (see below), whose sum is σ = 82813104. Its totient is φ = 80268480.

The previous prime is 81538577. The next prime is 81538609. The reversal of 81538591 is 19583518.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81538591 - 2²⁵ = 47984159 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 (81538991) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 68100 + ... + 69286.

It is an arithmetic number, because the mean of its divisors is an integer number (10351638).

Almost surely, 2^81538591 is an apocalyptic number.

81538591 is a deficient number, since it is larger than the sum of its proper divisors (1274513).

81538591 is a wasteful number, since it uses less digits than its factorization.

81538591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2201.

The product of its digits is 43200, while the sum is 40.

The square root of 81538591 is about 9029.8721474891. The cubic root of 81538591 is about 433.6317442905.

The spelling of 81538591 in words is "eighty-one million, five hundred thirty-eight thousand, five hundred ninety-one".