81815566 has 8 divisors (see below), whose sum is σ = 140255280. Its totient is φ = 35063808.

The previous prime is 81815563. The next prime is 81815581. The reversal of 81815566 is 66551818.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81815563) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2921971 + ... + 2921998.

It is an arithmetic number, because the mean of its divisors is an integer number (17531910).

Almost surely, 2^81815566 is an apocalyptic number.

81815566 is a deficient number, since it is larger than the sum of its proper divisors (58439714).

81815566 is a wasteful number, since it uses less digits than its factorization.

81815566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5843978.

The product of its digits is 57600, while the sum is 40.

The square root of 81815566 is about 9045.1957413867. The cubic root of 81815566 is about 434.1221845168.

It can be divided in two parts, 818 and 15566, that added together give a 14-th power (16384 = 2¹⁴).

The spelling of 81815566 in words is "eighty-one million, eight hundred fifteen thousand, five hundred sixty-six".