138531108721 has 2 divisors, whose sum is σ = 138531108722. Its totient is φ = 138531108720.

The previous prime is 138531108719. The next prime is 138531108743. The reversal of 138531108721 is 127801135831.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 136538379121 + 1992729600 = 369511^2 + 44640^2 .

It is a cyclic number.

It is not a de Polignac number, because 138531108721 - 2¹ = 138531108719 is a prime.

Together with 138531108719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (138531108761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69265554360 + 69265554361.

It is an arithmetic number, because the mean of its divisors is an integer number (69265554361).

Almost surely, 2^138531108721 is an apocalyptic number.

It is an amenable number.

138531108721 is a deficient number, since it is larger than the sum of its proper divisors (1).

138531108721 is an equidigital number, since it uses as much as digits as its factorization.

138531108721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40320, while the sum is 40.

The spelling of 138531108721 in words is "one hundred thirty-eight billion, five hundred thirty-one million, one hundred eight thousand, seven hundred twenty-one".