138640 has 20 divisors (see below), whose sum is σ = 322524. Its totient is φ = 55424.

The previous prime is 138637. The next prime is 138641. The reversal of 138640 is 46831.

It can be written as a sum of positive squares in 2 ways, for example, as 55696 + 82944 = 236^2 + 288^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (138641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 787 + ... + 946.

2¹³⁸⁶⁴⁰ is an apocalyptic number.

138640 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

138640 is an abundant number, since it is smaller than the sum of its proper divisors (183884).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

138640 is a wasteful number, since it uses less digits than its factorization.

138640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1746 (or 1740 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 22.

The square root of 138640 is about 372.3439270352. The cubic root of 138640 is about 51.7562557103.

Subtracting from 138640 its reverse (46831), we obtain a square (91809 = 303²).

The spelling of 138640 in words is "one hundred thirty-eight thousand, six hundred forty".