66601921 has 3 divisors (see below), whose sum is σ = 66610083. Its totient is φ = 66593760.

The previous prime is 66601901. The next prime is 66601967. The reversal of 66601921 is 12910666.

The square root of 66601921 is 8161.

It is a perfect power (a square), and thus also a powerful number.

66601921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 24611521 + 41990400 = 4961^2 + 6480^2 .

It is not a de Polignac number, because 66601921 - 2⁵ = 66601889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66601901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 4081 + ... + 12241.

It is an arithmetic number, because the mean of its divisors is an integer number (22203361).

Almost surely, 2^66601921 is an apocalyptic number.

66601921 is the 8161-st square number.

66601921 is the 4081-st centered octagonal number.

It is an amenable number.

66601921 is a deficient number, since it is larger than the sum of its proper divisors (8162).

66601921 is an frugal number, since it uses more digits than its factorization.

66601921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16322 (or 8161 counting only the distinct ones).

The product of its (nonzero) digits is 3888, while the sum is 31.

The cubic root of 66601921 is about 405.3488251133.

The spelling of 66601921 in words is "sixty-six million, six hundred one thousand, nine hundred twenty-one".