666139391 has 2 divisors, whose sum is σ = 666139392. Its totient is φ = 666139390.

The previous prime is 666139361. The next prime is 666139399. The reversal of 666139391 is 193931666.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 666139391 - 2¹⁰ = 666138367 is a prime.

It is equal to p_34588457 and since 666139391 and 34588457 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666139399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333069695 + 333069696.

It is an arithmetic number, because the mean of its divisors is an integer number (333069696).

Almost surely, 2^666139391 is an apocalyptic number.

666139391 is a deficient number, since it is larger than the sum of its proper divisors (1).

666139391 is an equidigital number, since it uses as much as digits as its factorization.

666139391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 157464, while the sum is 44.

The square root of 666139391 is about 25809.6763056029. The cubic root of 666139391 is about 873.3500951305.

The spelling of 666139391 in words is "six hundred sixty-six million, one hundred thirty-nine thousand, three hundred ninety-one".