138406 has 4 divisors (see below), whose sum is σ = 207612. Its totient is φ = 69202.

The previous prime is 138403. The next prime is 138407. The reversal of 138406 is 604831.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 604831 = 23 ⋅26297.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (138401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 34600 + ... + 34603.

It is an arithmetic number, because the mean of its divisors is an integer number (51903).

2¹³⁸⁴⁰⁶ is an apocalyptic number.

138406 is a deficient number, since it is larger than the sum of its proper divisors (69206).

138406 is an equidigital number, since it uses as much as digits as its factorization.

138406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69205.

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

The square root of 138406 is about 372.0295687173. The cubic root of 138406 is about 51.7271208190.

Subtracting from 138406 its sum of digits (22), we obtain a square (138384 = 372²).

It can be divided in two parts, 13 and 8406, that multiplied together give a triangular number (109278 = T₄₆₇).

The spelling of 138406 in words is "one hundred thirty-eight thousand, four hundred six".