165721 has 2 divisors, whose sum is σ = 165722. Its totient is φ = 165720.

The previous prime is 165719. The next prime is 165749. The reversal of 165721 is 127561.

165721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 151321 + 14400 = 389^2 + 120^2 .

It is a cyclic number.

It is not a de Polignac number, because 165721 - 2¹ = 165719 is a prime.

Together with 165719, it forms a pair of twin primes.

165721 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 165692 and 165701.

It is not a weakly prime, because it can be changed into another prime (165701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82860 + 82861.

It is an arithmetic number, because the mean of its divisors is an integer number (82861).

2¹⁶⁵⁷²¹ is an apocalyptic number.

It is an amenable number.

165721 is a deficient number, since it is larger than the sum of its proper divisors (1).

165721 is an equidigital number, since it uses as much as digits as its factorization.

165721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 420, while the sum is 22.

The square root of 165721 is about 407.0884424790. The cubic root of 165721 is about 54.9278392498.

The spelling of 165721 in words is "one hundred sixty-five thousand, seven hundred twenty-one".