165661 has 4 divisors (see below), whose sum is σ = 174400. Its totient is φ = 156924.

The previous prime is 165653. The next prime is 165667. The reversal of 165661 is 166561.

165661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 165661 - 2³ = 165653 is a prime.

It is a Duffinian number.

165661 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165667) 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, 4341 + ... + 4378.

It is an arithmetic number, because the mean of its divisors is an integer number (43600).

2¹⁶⁵⁶⁶¹ is an apocalyptic number.

It is an amenable number.

165661 is a deficient number, since it is larger than the sum of its proper divisors (8739).

165661 is an equidigital number, since it uses as much as digits as its factorization.

165661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8738.

The product of its digits is 1080, while the sum is 25.

The square root of 165661 is about 407.0147417478. The cubic root of 165661 is about 54.9212094962.

Subtracting 165661 from its reverse (166561), we obtain a square (900 = 30²).

The spelling of 165661 in words is "one hundred sixty-five thousand, six hundred sixty-one".