666625409 has 2 divisors, whose sum is σ = 666625410. Its totient is φ = 666625408.

The previous prime is 666625381. The next prime is 666625439. The reversal of 666625409 is 904526666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 555639184 + 110986225 = 23572^2 + 10535^2 .

It is a cyclic number.

It is not a de Polignac number, because 666625409 - 2²⁴ = 649848193 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 666625409.

It is not a weakly prime, because it can be changed into another prime (666625439) 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 as a sum of consecutive naturals, namely, 333312704 + 333312705.

It is an arithmetic number, because the mean of its divisors is an integer number (333312705).

Almost surely, 2^666625409 is an apocalyptic number.

It is an amenable number.

666625409 is a deficient number, since it is larger than the sum of its proper divisors (1).

666625409 is an equidigital number, since it uses as much as digits as its factorization.

666625409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 466560, while the sum is 44.

The square root of 666625409 is about 25819.0900110751. The cubic root of 666625409 is about 873.5624434187.

The spelling of 666625409 in words is "six hundred sixty-six million, six hundred twenty-five thousand, four hundred nine".