665720561 has 8 divisors (see below), whose sum is σ = 768960864. Its totient is φ = 569600320.

The previous prime is 665720557. The next prime is 665720569. The reversal of 665720561 is 165027566.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 665720561 - 2² = 665720557 is a prime.

It is not an unprimeable number, because it can be changed into a prime (665720569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1779815 + ... + 1780188.

It is an arithmetic number, because the mean of its divisors is an integer number (96120108).

Almost surely, 2^665720561 is an apocalyptic number.

It is an amenable number.

665720561 is a deficient number, since it is larger than the sum of its proper divisors (103240303).

665720561 is a wasteful number, since it uses less digits than its factorization.

665720561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3560031.

The product of its (nonzero) digits is 75600, while the sum is 38.

The square root of 665720561 is about 25801.5612124538. The cubic root of 665720561 is about 873.1670193791.

The spelling of 665720561 in words is "six hundred sixty-five million, seven hundred twenty thousand, five hundred sixty-one".