165681 has 12 divisors (see below), whose sum is σ = 245700. Its totient is φ = 107520.

The previous prime is 165673. The next prime is 165701. The reversal of 165681 is 186561.

165681 = T₁₈ + T₁₉ + ... + T₉₉.

165681 is a `hidden beast` number, since 1 + 656 + 8 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 46656 + 119025 = 216^2 + 345^2 .

It is not a de Polignac number, because 165681 - 2³ = 165673 is a prime.

It is a super-2 number, since 2×165681² = 54900387522, which contains 22 as substring.

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (165601) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 145 + ... + 593.

It is an arithmetic number, because the mean of its divisors is an integer number (20475).

2¹⁶⁵⁶⁸¹ is an apocalyptic number.

It is an amenable number.

165681 is a deficient number, since it is larger than the sum of its proper divisors (80019).

165681 is a wasteful number, since it uses less digits than its factorization.

165681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 496 (or 493 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 165681 is about 407.0393101409. The cubic root of 165681 is about 54.9234195919.

The spelling of 165681 in words is "one hundred sixty-five thousand, six hundred eighty-one".