165817721 has 2 divisors, whose sum is σ = 165817722. Its totient is φ = 165817720.

The previous prime is 165817699. The next prime is 165817727. The reversal of 165817721 is 127718561.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 146773225 + 19044496 = 12115^2 + 4364^2 .

It is a cyclic number.

It is not a de Polignac number, because 165817721 - 2¹⁰ = 165816697 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (165817727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 82908860 + 82908861.

It is an arithmetic number, because the mean of its divisors is an integer number (82908861).

Almost surely, 2^165817721 is an apocalyptic number.

It is an amenable number.

165817721 is a deficient number, since it is larger than the sum of its proper divisors (1).

165817721 is an equidigital number, since it uses as much as digits as its factorization.

165817721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23520, while the sum is 38.

The square root of 165817721 is about 12877.0229867000. The cubic root of 165817721 is about 549.3852315492.

The spelling of 165817721 in words is "one hundred sixty-five million, eight hundred seventeen thousand, seven hundred twenty-one".