165721408 has 14 divisors (see below), whose sum is σ = 328853546. Its totient is φ = 82860672.

The previous prime is 165721403. The next prime is 165721433. The reversal of 165721408 is 804127561.

It can be written as a sum of positive squares in only one way, i.e., 139996224 + 25725184 = 11832^2 + 5072^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165721403) 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, 1294635 + ... + 1294762.

It is an arithmetic number, because the mean of its divisors is an integer number (23489539).

Almost surely, 2^165721408 is an apocalyptic number.

It is an amenable number.

165721408 is a deficient number, since it is larger than the sum of its proper divisors (163132138).

165721408 is an equidigital number, since it uses as much as digits as its factorization.

165721408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2589409 (or 2589399 counting only the distinct ones).

The product of its (nonzero) digits is 13440, while the sum is 34.

The square root of 165721408 is about 12873.2827204253. The cubic root of 165721408 is about 549.2788432666.

Adding to 165721408 its reverse (804127561), we get a palindrome (969848969).

The spelling of 165721408 in words is "one hundred sixty-five million, seven hundred twenty-one thousand, four hundred eight".