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138 (one hundred [and] thirty-eight) is the natural number following 137 and preceding 139.
138 is a sphenic number, the sum of four consecutive primes (29 + 31 + 37 + 41), and the smallest product of three primes, such that in base 10, the third prime is a concatenation of the other two: .
138 is the third 47-gonal number and an Ulam number, as well as a one step palindrome (138 + 831 = 969.)
138 is the 72nd normal congruent number and the 49th primitive or square free congruent number.
In the military
In other fields
138 is also: