165686021 has 2 divisors, whose sum is σ = 165686022. Its totient is φ = 165686020.

The previous prime is 165685999. The next prime is 165686047. The reversal of 165686021 is 120686561.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 110481121 + 55204900 = 10511^2 + 7430^2 .

It is a cyclic number.

It is not a de Polignac number, because 165686021 - 2⁶ = 165685957 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (165686051) 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 as a sum of consecutive naturals, namely, 82843010 + 82843011.

It is an arithmetic number, because the mean of its divisors is an integer number (82843011).

Almost surely, 2^165686021 is an apocalyptic number.

It is an amenable number.

165686021 is a deficient number, since it is larger than the sum of its proper divisors (1).

165686021 is an equidigital number, since it uses as much as digits as its factorization.

165686021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 165686021 is about 12871.9082112949. The cubic root of 165686021 is about 549.2397440854.

The spelling of 165686021 in words is "one hundred sixty-five million, six hundred eighty-six thousand, twenty-one".