66765721 has 4 divisors (see below), whose sum is σ = 72835344. Its totient is φ = 60696100.

The previous prime is 66765697. The next prime is 66765739. The reversal of 66765721 is 12756766.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 66765721 - 2⁷ = 66765593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66765121) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3034795 + ... + 3034816.

It is an arithmetic number, because the mean of its divisors is an integer number (18208836).

Almost surely, 2^66765721 is an apocalyptic number.

It is an amenable number.

66765721 is a deficient number, since it is larger than the sum of its proper divisors (6069623).

66765721 is a wasteful number, since it uses less digits than its factorization.

66765721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6069622.

The product of its digits is 105840, while the sum is 40.

The square root of 66765721 is about 8171.0293721171. The cubic root of 66765721 is about 405.6808564797.

The spelling of 66765721 in words is "sixty-six million, seven hundred sixty-five thousand, seven hundred twenty-one".