66657809 has 4 divisors (see below), whose sum is σ = 66868404. Its totient is φ = 66447216.

The previous prime is 66657803. The next prime is 66657821. The reversal of 66657809 is 90875666.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9610000 + 57047809 = 3100^2 + 7553^2 .

It is a cyclic number.

It is not a de Polignac number, because 66657809 - 2²⁰ = 65609233 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66657803) 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, 104822 + ... + 105455.

It is an arithmetic number, because the mean of its divisors is an integer number (16717101).

Almost surely, 2^66657809 is an apocalyptic number.

It is an amenable number.

66657809 is a deficient number, since it is larger than the sum of its proper divisors (210595).

66657809 is a wasteful number, since it uses less digits than its factorization.

66657809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 210594.

The product of its (nonzero) digits is 544320, while the sum is 47.

The square root of 66657809 is about 8164.4233721678. The cubic root of 66657809 is about 405.4621742035.

The spelling of 66657809 in words is "sixty-six million, six hundred fifty-seven thousand, eight hundred nine".