81391823 has 8 divisors (see below), whose sum is σ = 83781792. Its totient is φ = 79011936.

The previous prime is 81391813. The next prime is 81391831. The reversal of 81391823 is 32819318.

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 81391823 - 2¹⁸ = 81129679 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 (81391813) 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, 15761 + ... + 20277.

It is an arithmetic number, because the mean of its divisors is an integer number (10472724).

Almost surely, 2^81391823 is an apocalyptic number.

81391823 is a deficient number, since it is larger than the sum of its proper divisors (2389969).

81391823 is a wasteful number, since it uses less digits than its factorization.

81391823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5041.

The product of its digits is 10368, while the sum is 35.

The square root of 81391823 is about 9021.7416832893. The cubic root of 81391823 is about 433.3714115782.

The spelling of 81391823 in words is "eighty-one million, three hundred ninety-one thousand, eight hundred twenty-three".