39 (number)

Script error: No such module "redirect hatnote". Template:Infobox number 39 (thirty-nine) is the natural number following 38 and preceding 40.

In mathematics

The F26A graph has 39 edges, all equivalent.

39 is the 12th distinct semiprime^[1] and the 4th in the (3.q) family.^[2] It is the last member of the third distinct semiprime pair (38,39).
39 has an aliquot sum of 17, which is a prime. 39 is the 4th member of the 17-aliquot tree within an aliquot sequence of one composite numbers (39,17,1,0) to the Prime in the 17-aliquot tree.
It is a perfect totient number.^[3]
39 is the sum of five consecutive primes (3 + 5 + 7 + 11 + 13) and also is the product of the first and the last of those consecutive primes. Among small semiprimes only three other integers (10, 155, and 371) share this attribute. 39 also is the sum of the first three powers of 3 (3¹ + 3² + 3³). Given 39, the Mertens function returns 0.^[4]
39 is the smallest natural number which has three partitions into three parts which all give the same product when multiplied: {25, 8, 6}, {24, 10, 5}, {20, 15, 4}.

39 is a Perrin number, coming after 17, 22, 29 (it is the sum of the first two mentioned).^[5]
Since the greatest prime factor of 39² + 1 = 1522 is 761, which is more than 39 twice, 39 is a Størmer number.^[6]
The F26A graph is a symmetric graph with 39 edges.

Japanese wordplay and slang:
- Through numeric substitution, 39 is the Internet chat slang term for "Thank you" when written with numbers: Template:Jp and Template:Jp.^[7]
- 39 has also been associated with the virtual singer Hatsune Miku for the same reason: Template:Jp can also be read as Template:Jp,^[8] and Template:Jp can also be read as Template:Jp.^[9] Thus, if using the alternative readings, Template:Jp can also be read as Template:Jp.^[10]^[11]

In Afghanistan, the number 39 is considered unlucky, due to the belief that it is associated with pimps. See Curse of 39.^[12]