666819217 has 4 divisors (see below), whose sum is σ = 684841396. Its totient is φ = 648797040.

The previous prime is 666819191. The next prime is 666819233. The reversal of 666819217 is 712918666.

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 646379776 + 20439441 = 25424^2 + 4521^2 .

It is a cyclic number.

It is not a de Polignac number, because 666819217 - 2¹⁹ = 666294929 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (666819277) 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, 9011034 + ... + 9011107.

It is an arithmetic number, because the mean of its divisors is an integer number (171210349).

Almost surely, 2^666819217 is an apocalyptic number.

It is an amenable number.

666819217 is a deficient number, since it is larger than the sum of its proper divisors (18022179).

666819217 is a wasteful number, since it uses less digits than its factorization.

666819217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18022178.

The product of its digits is 217728, while the sum is 46.

The square root of 666819217 is about 25822.8429302430. The cubic root of 666819217 is about 873.6470921501.

The spelling of 666819217 in words is "six hundred sixty-six million, eight hundred nineteen thousand, two hundred seventeen".