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 A023200 Primes p such that p + 4 is also prime. 126
 3, 7, 13, 19, 37, 43, 67, 79, 97, 103, 109, 127, 163, 193, 223, 229, 277, 307, 313, 349, 379, 397, 439, 457, 463, 487, 499, 613, 643, 673, 739, 757, 769, 823, 853, 859, 877, 883, 907, 937, 967, 1009, 1087, 1093, 1213, 1279, 1297, 1303, 1423, 1429, 1447, 1483 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Smaller member p of cousin prime pairs (p, p+4). A015913 contains the composite number 305635357, so it is different from both the present sequence and A029710. (305635357 is the only composite member of A015913 < 10^9.) - Jud McCranie, Jan 07 2001 Apart from the first term, all terms are of the form 6n + 1. Complement of A067775 (primes p such that p + 4 is composite) with respect to A000040 (primes). With prime 2 also primes p such that q^2 + p is prime for some prime q (q = 3 if p = 2, q = 2 if p > 2). Subsequence of A232012. - Jaroslav Krizek, Nov 23 2013 Conjecture: The sequence is infinite and for every n, a(n+1) < a(n)^(1+1/n). Namely a(n)^(1/n) is a strictly decreasing function of n. - Jahangeer Kholdi and Farideh Firoozbakht, Nov 24 2014 From Alonso del Arte, Jan 12 2019: (Start) If p splits in Z[sqrt(-2)], p + 4 is an inert prime in that domain. Likewise, if p splits in Z[sqrt(2)], p + 4 is an inert prime in that domain. The only way for p or p + 4 to split in both domains is if it is congruent to 1 modulo 24, in which case the other prime is inert in both domains. For example, 3 = (1 - sqrt(-2))*(1 + sqrt(-2)) but is inert in Z[sqrt(2)], while 7 = (3 - sqrt(2))*(3 + sqrt(2)) but is inert in Z[sqrt(-2)]. And also 11 = (3 - sqrt(-2))*(3 + sqrt(-2)) but 15 is composite in Z or any quadratic integer ring. And 97 = (5 - 6*sqrt(-2))*(5 + 6*sqrt(-2)) = (1 - 7*sqrt(2))*(1 + 7*sqrt(2)), but 101 is inert in both Z[sqrt(-2)] and Z[sqrt(2)]. (End) LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 Andrew Granville and Greg Martin, Prime number races, arXiv:math/0408319 [math.NT], 2004. Maxie D. Schmidt, New Congruences and Finite Difference Equations for Generalized Factorial Functions, arXiv:1701.04741 [math.CO], 2017. H. J. Weber, A Sieve for Cousin Primes, arXiv:1204.3795v1 [math.NT], 2012. Eric Weisstein's World of Mathematics, Cousin Primes Eric Weisstein's World of Mathematics, Twin Primes FORMULA a(n) = A046132(n) - 4 = A087679(n) - 2. a(n) >> n log^2 n via the Selberg sieve. - Charles R Greathouse IV, Nov 20 2016 MAPLE A023200 := proc(n) option remember; if n = 1 then 3; else p := nextprime(procname(n-1)) ; while not isprime(p+4) do p := nextprime(p) ;  end do: p ; end if; end proc: # R. J. Mathar, Sep 03 2011 MATHEMATICA Select[Range[10^2], PrimeQ[#] && PrimeQ[# + 4] &] (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 *) PROG (PARI) print1(3); p=7; forprime(q=11, 1e3, if(q-p==4, print1(", "p)); p=q) \\ Charles R Greathouse IV, Mar 20 2013 (MAGMA) [p: p in PrimesUpTo(1500) | NextPrime(p)-p eq 4]; // Bruno Berselli, Apr 09 2013 (Haskell) a023200 n = a023200_list !! (n-1) a023200_list = filter ((== 1) . a010051') \$                map (subtract 4) \$ drop 2 a000040_list -- Reinhard Zumkeller, Aug 01 2014 CROSSREFS Exactly the same as A029710 except for the exclusion of 3. Cf. A000010, A003557, A007947, A046132, A098429, A000040, A010051. Sequence in context: A216518 A154650 A015913 * A046136 A098044 A252091 Adjacent sequences:  A023197 A023198 A023199 * A023201 A023202 A023203 KEYWORD nonn AUTHOR EXTENSIONS Definition modified by Vincenzo Librandi, Aug 02 2009 Definition revised by N. J. A. Sloane, Mar 05 2010 STATUS approved

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Last modified October 15 22:25 EDT 2019. Contains 328038 sequences. (Running on oeis4.)