38 (thirty-eight) is the natural number following 37 and preceding 39.

In mathematics

• specifically, the 11th discrete Semiprime,^[1] it being the 7th of the form (2.q).
• the first member of the third cluster of two discrete semiprimes 38, 39 the next such cluster is 57, 58.
• with an aliquot sum of 22 in an aliquot sequence of five composite numbers (38,22,14,10,8,7,1,0) to the Prime in the 7-aliquot tree. 34 is the first semiprime within a chain of 4 semiprimes in its aliquot sequence (38,22,14,10). The next semiprime with a four semiprime chain is 166.
• 38! − 1 yields 523022617466601111760007224100074291199999999 which is the 16th factorial prime.^[2]
• There is no answer to the equation φ(x) = 38, making 38 a nontotient.^[3]
• 38 is the sum of the squares of the first three primes.
• 37 and 38 are the first pair of consecutive positive integers not divisible by any of their digits.
• 38 is the largest even number which cannot be written as the sum of two odd composite numbers.
• The sum of each row of the only non-trivial (order 3) magic hexagon is 38.^[4]

In science

• The atomic number of strontium

Astronomy

• The Messier object M38, a magnitude 7.0 open cluster in the constellation Auriga
• The New General Catalogue object NGC 38, a spiral galaxy in the constellation Pisces

In other fields

Thirty-eight is also:

• The 38th parallel north is the pre-Korean War boundary between North Korea and South Korea.^[5]
• The number of slots on an American roulette wheel (0, 00, and 1 through 36; European roulette does not use the 00 slot and has only 37 slots)
• The Ishihara test is a color vision test consisting of 38 pseudoisochromatic plates.^[6]
• A "38" is often the name for a snub nose .38 caliber revolver.
• The 38 class is the most famous class of steam locomotive used in New South Wales
• Gerald Ford, 38th President of the United States
• Arnold Schwarzenegger, 38th Governor of California, most recent Republican governor of California, and the second governor to be born outside of the United States
• Cats have a total of 38 chromosomes in their genome.
• Number used by Zane Smith and Front Row Motorsports to win the 2022 NASCAR Camping World Truck Series championship.
• The Lucky 38, the casino from Fallout: New Vegas.