165560721 has 4 divisors (see below), whose sum is σ = 220747632. Its totient is φ = 110373812.

The previous prime is 165560719. The next prime is 165560723. The reversal of 165560721 is 127065561.

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 an interprime number because it is at equal distance from previous prime (165560719) and next prime (165560723).

It is a cyclic number.

It is not a de Polignac number, because 165560721 - 2¹ = 165560719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (165560723) 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, 27593451 + ... + 27593456.

It is an arithmetic number, because the mean of its divisors is an integer number (55186908).

Almost surely, 2^165560721 is an apocalyptic number.

It is an amenable number.

165560721 is a deficient number, since it is larger than the sum of its proper divisors (55186911).

165560721 is an equidigital number, since it uses as much as digits as its factorization.

165560721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55186910.

The product of its (nonzero) digits is 12600, while the sum is 33.

The square root of 165560721 is about 12867.0401025255. The cubic root of 165560721 is about 549.1012550422.

The spelling of 165560721 in words is "one hundred sixty-five million, five hundred sixty thousand, seven hundred twenty-one".