2181165581 has 4 divisors (see below), whose sum is σ = 2492760672. Its totient is φ = 1869570492.

The previous prime is 2181165563. The next prime is 2181165641. The reversal of 2181165581 is 1855611812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 2181165581 - 2¹⁴ = 2181149197 is a prime.

It is a super-2 number, since 2×2181165581² = 9514966583478135122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2181165521) 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, 155797535 + ... + 155797548.

It is an arithmetic number, because the mean of its divisors is an integer number (623190168).

Almost surely, 2^2181165581 is an apocalyptic number.

It is an amenable number.

2181165581 is a deficient number, since it is larger than the sum of its proper divisors (311595091).

2181165581 is an equidigital number, since it uses as much as digits as its factorization.

2181165581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 311595090.

The product of its digits is 19200, while the sum is 38.

The square root of 2181165581 is about 46702.9504528354. The cubic root of 2181165581 is about 1296.8693070721.

The spelling of 2181165581 in words is "two billion, one hundred eighty-one million, one hundred sixty-five thousand, five hundred eighty-one".