165686561 has 4 divisors (see below), whose sum is σ = 167327124. Its totient is φ = 164046000.

The previous prime is 165686557. The next prime is 165686569.

165686561 is nontrivially palindromic in base 10.

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 85673536 + 80013025 = 9256^2 + 8945^2 .

It is a cyclic number.

It is not a de Polignac number, because 165686561 - 2² = 165686557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165686569) 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, 820130 + ... + 820331.

It is an arithmetic number, because the mean of its divisors is an integer number (41831781).

Almost surely, 2^165686561 is an apocalyptic number.

It is an amenable number.

165686561 is a deficient number, since it is larger than the sum of its proper divisors (1640563).

165686561 is a wasteful number, since it uses less digits than its factorization.

165686561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1640562.

The product of its digits is 259200, while the sum is 44.

The square root of 165686561 is about 12871.9291871887. The cubic root of 165686561 is about 549.2403407745.

The spelling of 165686561 in words is "one hundred sixty-five million, six hundred eighty-six thousand, five hundred sixty-one".