66647101921 has 3 divisors (see below), whose sum is σ = 66647360083. Its totient is φ = 66646843760.

The previous prime is 66647101889. The next prime is 66647101949. The reversal of 66647101921 is 12910174666.

The square root of 66647101921 is 258161.

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

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., 63448068321 + 3199033600 = 251889^2 + 56560^2 .

It is not a de Polignac number, because 66647101921 - 2⁵ = 66647101889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66647101951) 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 2 ways as a sum of consecutive naturals, for example, 129081 + ... + 387241.

Almost surely, 2^66647101921 is an apocalyptic number.

66647101921 is the 258161-st square number.

66647101921 is the 129081-st centered octagonal number.

It is an amenable number.

66647101921 is a deficient number, since it is larger than the sum of its proper divisors (258162).

66647101921 is an frugal number, since it uses more digits than its factorization.

66647101921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 516322 (or 258161 counting only the distinct ones).

The product of its (nonzero) digits is 108864, while the sum is 43.

The spelling of 66647101921 in words is "sixty-six billion, six hundred forty-seven million, one hundred one thousand, nine hundred twenty-one".