81855091 has 4 divisors (see below), whose sum is σ = 85414032. Its totient is φ = 78296152.

The previous prime is 81855079. The next prime is 81855113. The reversal of 81855091 is 19055818.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19055818 = 2 ⋅9527909.

It is a cyclic number.

It is not a de Polignac number, because 81855091 - 2⁷ = 81854963 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81855091.

It is not an unprimeable number, because it can be changed into a prime (81855031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1779436 + ... + 1779481.

It is an arithmetic number, because the mean of its divisors is an integer number (21353508).

Almost surely, 2^81855091 is an apocalyptic number.

81855091 is a deficient number, since it is larger than the sum of its proper divisors (3558941).

81855091 is a wasteful number, since it uses less digits than its factorization.

81855091 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3558940.

The product of its (nonzero) digits is 14400, while the sum is 37.

The square root of 81855091 is about 9047.3803390816. The cubic root of 81855091 is about 434.1920812280.

The spelling of 81855091 in words is "eighty-one million, eight hundred fifty-five thousand, ninety-one".