81645891 has 8 divisors (see below), whose sum is σ = 109592400. Its totient is φ = 54064992.

The previous prime is 81645871. The next prime is 81645899. The reversal of 81645891 is 19854618.

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

It is not a de Polignac number, because 81645891 - 2⁵ = 81645859 is a prime.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (81645899) 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, 90880 + ... + 91773.

It is an arithmetic number, because the mean of its divisors is an integer number (13699050).

Almost surely, 2^81645891 is an apocalyptic number.

81645891 is a deficient number, since it is larger than the sum of its proper divisors (27946509).

81645891 is a wasteful number, since it uses less digits than its factorization.

81645891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182805.

The product of its digits is 69120, while the sum is 42.

The square root of 81645891 is about 9035.8115850210. The cubic root of 81645891 is about 433.8218722239.

The spelling of 81645891 in words is "eighty-one million, six hundred forty-five thousand, eight hundred ninety-one".