138409 has 4 divisors (see below), whose sum is σ = 140740. Its totient is φ = 136080.

The previous prime is 138407. The next prime is 138427. The reversal of 138409 is 904831.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 904831 = 479 ⋅1889.

It can be written as a sum of positive squares in 2 ways, for example, as 5184 + 133225 = 72^2 + 365^2 .

It is a cyclic number.

It is not a de Polignac number, because 138409 - 2¹ = 138407 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 (138401) 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, 1074 + ... + 1195.

It is an arithmetic number, because the mean of its divisors is an integer number (35185).

2¹³⁸⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

138409 is a deficient number, since it is larger than the sum of its proper divisors (2331).

138409 is an equidigital number, since it uses as much as digits as its factorization.

138409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2330.

The product of its (nonzero) digits is 864, while the sum is 25.

The square root of 138409 is about 372.0336006331. The cubic root of 138409 is about 51.7274945510.

Subtracting from 138409 its sum of digits (25), we obtain a square (138384 = 372²).

The spelling of 138409 in words is "one hundred thirty-eight thousand, four hundred nine".