666400109 has 2 divisors, whose sum is σ = 666400110. Its totient is φ = 666400108.

The previous prime is 666400099. The next prime is 666400123. The reversal of 666400109 is 901004666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 378419209 + 287980900 = 19453^2 + 16970^2 .

It is a cyclic number.

It is not a de Polignac number, because 666400109 - 2¹² = 666396013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666403109) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333200054 + 333200055.

It is an arithmetic number, because the mean of its divisors is an integer number (333200055).

Almost surely, 2^666400109 is an apocalyptic number.

It is an amenable number.

666400109 is a deficient number, since it is larger than the sum of its proper divisors (1).

666400109 is an equidigital number, since it uses as much as digits as its factorization.

666400109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7776, while the sum is 32.

The square root of 666400109 is about 25814.7265916182. The cubic root of 666400109 is about 873.4640194301.

The spelling of 666400109 in words is "six hundred sixty-six million, four hundred thousand, one hundred nine".