668820809 has 4 divisors (see below), whose sum is σ = 668907204. Its totient is φ = 668734416.

The previous prime is 668820799. The next prime is 668820811. The reversal of 668820809 is 908028866.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 908028866 = 2 ⋅454014433.

It can be written as a sum of positive squares in 2 ways, for example, as 501894409 + 166926400 = 22403^2 + 12920^2 .

It is a cyclic number.

It is not a de Polignac number, because 668820809 - 2⁸ = 668820553 is a prime.

It is a super-3 number, since 3×668820809³ (a number of 27 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (668820829) 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 3 ways as a sum of consecutive naturals, for example, 30302 + ... + 47495.

It is an arithmetic number, because the mean of its divisors is an integer number (167226801).

Almost surely, 2^668820809 is an apocalyptic number.

It is an amenable number.

668820809 is a deficient number, since it is larger than the sum of its proper divisors (86395).

668820809 is an equidigital number, since it uses as much as digits as its factorization.

668820809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86394.

The product of its (nonzero) digits is 331776, while the sum is 47.

The square root of 668820809 is about 25861.5701186142. The cubic root of 668820809 is about 874.5203614567.

The spelling of 668820809 in words is "six hundred sixty-eight million, eight hundred twenty thousand, eight hundred nine".