138539561 has 2 divisors, whose sum is σ = 138539562. Its totient is φ = 138539560.

The previous prime is 138539543. The next prime is 138539563. The reversal of 138539561 is 165935831.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 125865961 + 12673600 = 11219^2 + 3560^2 .

It is a cyclic number.

It is not a de Polignac number, because 138539561 - 2⁶ = 138539497 is a prime.

It is a Sophie Germain prime.

Together with 138539563, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (138539563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69269780 + 69269781.

It is an arithmetic number, because the mean of its divisors is an integer number (69269781).

Almost surely, 2^138539561 is an apocalyptic number.

It is an amenable number.

138539561 is a deficient number, since it is larger than the sum of its proper divisors (1).

138539561 is an equidigital number, since it uses as much as digits as its factorization.

138539561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 97200, while the sum is 41.

The square root of 138539561 is about 11770.2829617643. The cubic root of 138539561 is about 517.4375426190.

The spelling of 138539561 in words is "one hundred thirty-eight million, five hundred thirty-nine thousand, five hundred sixty-one".