2166006581 has 4 divisors (see below), whose sum is σ = 2169097164. Its totient is φ = 2162916000.

The previous prime is 2166006553. The next prime is 2166006599. The reversal of 2166006581 is 1856006612.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1727732356 + 438274225 = 41566^2 + 20935^2 .

It is a cyclic number.

It is not a de Polignac number, because 2166006581 - 2²² = 2161812277 is a prime.

It is a super-2 number, since 2×2166006581² = 9383169017870619122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2166006541) 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 3 ways as a sum of consecutive naturals, for example, 1544240 + ... + 1545641.

It is an arithmetic number, because the mean of its divisors is an integer number (542274291).

Almost surely, 2^2166006581 is an apocalyptic number.

It is an amenable number.

2166006581 is a deficient number, since it is larger than the sum of its proper divisors (3090583).

2166006581 is an equidigital number, since it uses as much as digits as its factorization.

2166006581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3090582.

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 2166006581 is about 46540.3758149846. The cubic root of 2166006581 is about 1293.8579260210.

The spelling of 2166006581 in words is "two billion, one hundred sixty-six million, six thousand, five hundred eighty-one".