138987791 has 4 divisors (see below), whose sum is σ = 139030584. Its totient is φ = 138945000.

The previous prime is 138987763. The next prime is 138987811. The reversal of 138987791 is 197789831.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 197789831 = 29 ⋅6820339.

It is a cyclic number.

It is not a de Polignac number, because 138987791 - 2²⁶ = 71878927 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (138987701) 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 in 3 ways as a sum of consecutive naturals, for example, 16085 + ... + 23166.

It is an arithmetic number, because the mean of its divisors is an integer number (34757646).

Almost surely, 2^138987791 is an apocalyptic number.

138987791 is a deficient number, since it is larger than the sum of its proper divisors (42793).

138987791 is an equidigital number, since it uses as much as digits as its factorization.

138987791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42792.

The product of its digits is 762048, while the sum is 53.

The square root of 138987791 is about 11789.3083342493. The cubic root of 138987791 is about 517.9949799010.

The spelling of 138987791 in words is "one hundred thirty-eight million, nine hundred eighty-seven thousand, seven hundred ninety-one".