#jsDisabledContent { display:none; } My Account | Register | Help

# Cousin prime

Article Id: WHEBN0000343085
Reproduction Date:

 Title: Cousin prime Author: World Heritage Encyclopedia Language: English Subject: Collection: Publisher: World Heritage Encyclopedia Publication Date:

### Cousin prime

In mathematics, cousin primes are prime numbers that differ by four.[1] Compare this with twin primes, pairs of prime numbers that differ by two, and sexy primes, pairs of prime numbers that differ by six.

The cousin primes (sequences  A023200 and  A046132 in OEIS) below 1000 are:

(3, 7), (7, 11), (13, 17), (19, 23), (37, 41), (43, 47), (67, 71), (79, 83), (97, 101), (103, 107), (109, 113), (127, 131), (163, 167), (193, 197), (223, 227), (229, 233), (277, 281), (307, 311), (313, 317), (349, 353), (379, 383), (397, 401), (439, 443), (457, 461), (463,467), (487, 491), (499, 503), (613, 617), (643, 647), (673, 677), (739, 743), (757, 761), (769, 773), (823, 827), (853, 857), (859, 863), (877, 881), (883, 887), (907, 911), (937, 941), (967, 971)

## Properties

The only prime belonging to two pairs of cousin primes is 7. One of the numbers nn+4, n+8 will always be divisible by 3, so n = 3 is the only case where all three are primes.

As of May 2009 the largest known cousin prime was (pp + 4) for

p = (311778476 · 587502 · 9001# · (587502 · 9001# + 1) + 210)·(587502 · 9001# − 1)/35 + 1

where 9001# is a primorial. It was found by Ken Davis and has 11594 digits.[2]

The largest known cousin probable prime is

474435381 · 298394 − 1
474435381 · 298394 − 5.

It has 29629 digits and was found by Angel, Jobling and Augustin.[3] While the first of these numbers has been proven prime, there is no known primality test to easily determine whether the second number is prime.

It follows from the first Hardy–Littlewood conjecture that cousin primes have the same asymptotic density as twin primes. An analogue of Brun's constant for twin primes can be defined for cousin primes, called Brun's constant for cousin primes, with the initial term (3, 7) omitted, bu the convergent sum:[4]

B_4 = \left(\frac{1}{7} + \frac{1}{11}\right) + \left(\frac{1}{13} + \frac{1}{17}\right) + \left(\frac{1}{19} + \frac{1}{23}\right) + \cdots.

Using cousin primes up to 242, the value of B4 was estimated by Marek Wolf in 1996 as

B4 ≈ 1.1970449.[5]

This constant should not be confused with Brun's constant for prime quadruplets, which is also denoted B4.

## Linguistic note

In Portuguese and Spanish the same word primo serves to designate both cousin and prime, so a literal translation would be Número primo primo.

## References

1. ^ Weisstein, Eric W., "Cousin Primes", MathWorld.
2. ^ Davis, Ken (2009-05-08). "11594 digit cousin prime pair". primenumbers (Mailing list). Retrieved 2009-05-09.
3. ^ − 198394474435381 · 2. Prime pages.
4. ^ Segal, B. (1930). "Generalisation du théorème de Brun". C. R. Acad. Sc. URSS (in Russian) 1930: 501–507.
5. ^ Marek Wolf, On the Twin and Cousin Primes (PostScript file).
• Wells, David (2011). Prime Numbers: The Most Mysterious Figures in Math. John Wiley & Sons. p. 33.
• Fine, Benjamin; Rosenberger, Gerhard (2007). Number theory: an introduction via the distribution of primes. Birkhäuser. p. 206.
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.

Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.