138509281 has 4 divisors (see below), whose sum is σ = 138532864. Its totient is φ = 138485700.

The previous prime is 138509257. The next prime is 138509291. The reversal of 138509281 is 182905831.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 138509281 - 2⁷ = 138509153 is a prime.

It is a super-2 number, since 2×138509281² = 38369641846273922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 138509281.

It is not an unprimeable number, because it can be changed into a prime (138509291) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4816 + ... + 17326.

It is an arithmetic number, because the mean of its divisors is an integer number (34633216).

Almost surely, 2^138509281 is an apocalyptic number.

It is an amenable number.

138509281 is a deficient number, since it is larger than the sum of its proper divisors (23583).

138509281 is a wasteful number, since it uses less digits than its factorization.

138509281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23582.

The product of its (nonzero) digits is 17280, while the sum is 37.

The square root of 138509281 is about 11768.9966012401. The cubic root of 138509281 is about 517.3998418345.

The spelling of 138509281 in words is "one hundred thirty-eight million, five hundred nine thousand, two hundred eighty-one".