138915209 has 2 divisors, whose sum is σ = 138915210. Its totient is φ = 138915208.

The previous prime is 138915169. The next prime is 138915229. The reversal of 138915209 is 902519831.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 125372809 + 13542400 = 11197^2 + 3680^2 .

It is a cyclic number.

It is not a de Polignac number, because 138915209 - 2⁸ = 138914953 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 (138915229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69457604 + 69457605.

It is an arithmetic number, because the mean of its divisors is an integer number (69457605).

Almost surely, 2^138915209 is an apocalyptic number.

It is an amenable number.

138915209 is a deficient number, since it is larger than the sum of its proper divisors (1).

138915209 is an equidigital number, since it uses as much as digits as its factorization.

138915209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 19440, while the sum is 38.

The square root of 138915209 is about 11786.2296346202. The cubic root of 138915209 is about 517.9047953414.

The spelling of 138915209 in words is "one hundred thirty-eight million, nine hundred fifteen thousand, two hundred nine".