• 138 can be written using four 4's:
138 is nontrivially palindromic in base 8.
138 is an esthetic number in base 8, because in such base its adjacent digits differ by 1.
It is a sphenic number, since it is the product of 3 distinct primes.
138 is an admirable number.
It is an Ulam number.
138 is an undulating number in base 8.
It is a Curzon number.
It is a plaindrome in base 7, base 10, base 11, base 14 and base 16.
It is a nialpdrome in base 12, base 13 and base 15.
It is a congruent number.
138 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
138 is a wasteful number, since it uses less digits than its factorization.
138 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 28.
The square root of 138 is about 11.7473401245. The cubic root of 138 is about 5.1676492524.
Adding to 138 its reverse (831), we get a palindrome (969).
The spelling of 138 in words is "one hundred thirty-eight", and thus it is an aban number.