81931591 has 8 divisors (see below), whose sum is σ = 98564480. Its totient is φ = 66530808.

The previous prime is 81931573. The next prime is 81931631. The reversal of 81931591 is 19513918.

It is a happy number.

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 81931591 - 2⁵ = 81931559 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81931591.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81931501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 307881 + ... + 308146.

It is an arithmetic number, because the mean of its divisors is an integer number (12320560).

Almost surely, 2^81931591 is an apocalyptic number.

81931591 is a deficient number, since it is larger than the sum of its proper divisors (16632889).

81931591 is a wasteful number, since it uses less digits than its factorization.

81931591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 616053.

The product of its digits is 9720, while the sum is 37.

The square root of 81931591 is about 9051.6070948755. The cubic root of 81931591 is about 434.3273012924.

The spelling of 81931591 in words is "eighty-one million, nine hundred thirty-one thousand, five hundred ninety-one".