138649891 has 4 divisors (see below), whose sum is σ = 139662072. Its totient is φ = 137637712.

The previous prime is 138649883. The next prime is 138649921. The reversal of 138649891 is 198946831.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 138649891 - 2³ = 138649883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (138649811) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 505885 + ... + 506158.

It is an arithmetic number, because the mean of its divisors is an integer number (34915518).

Almost surely, 2^138649891 is an apocalyptic number.

138649891 is a deficient number, since it is larger than the sum of its proper divisors (1012181).

138649891 is a wasteful number, since it uses less digits than its factorization.

138649891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1012180.

The product of its digits is 373248, while the sum is 49.

The square root of 138649891 is about 11774.9688322305. The cubic root of 138649891 is about 517.5748649732.

The spelling of 138649891 in words is "one hundred thirty-eight million, six hundred forty-nine thousand, eight hundred ninety-one".