669921809 has 2 divisors, whose sum is σ = 669921810. Its totient is φ = 669921808.

The previous prime is 669921787. The next prime is 669921827. The reversal of 669921809 is 908129966.

669921809 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 339591184 + 330330625 = 18428^2 + 18175^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-669921809 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (669921859) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334960904 + 334960905.

It is an arithmetic number, because the mean of its divisors is an integer number (334960905).

Almost surely, 2^669921809 is an apocalyptic number.

It is an amenable number.

669921809 is a deficient number, since it is larger than the sum of its proper divisors (1).

669921809 is an equidigital number, since it uses as much as digits as its factorization.

669921809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 419904, while the sum is 50.

The square root of 669921809 is about 25882.8477760852. The cubic root of 669921809 is about 874.9999712653. Note that the first 4 decimals are identical.

The spelling of 669921809 in words is "six hundred sixty-nine million, nine hundred twenty-one thousand, eight hundred nine".