cp's OEIS Frontend

A003627 Primes of the form 3n-1.

%I A003627 M1388 #135 Feb 16 2025 08:32:27
%S A003627 2,5,11,17,23,29,41,47,53,59,71,83,89,101,107,113,131,137,149,167,173,
%T A003627 179,191,197,227,233,239,251,257,263,269,281,293,311,317,347,353,359,
%U A003627 383,389,401,419,431,443,449,461,467,479,491,503,509,521,557,563,569,587
%N A003627 Primes of the form 3n-1.
%C A003627 Inert rational primes in the field Q(sqrt(-3)). - _N. J. A. Sloane_, Dec 25 2017
%C A003627 Primes p such that 1+x+x^2 is irreducible over GF(p). - _Joerg Arndt_, Aug 10 2011
%C A003627 Primes p dividing sum(k=0,p,C(2k,k)) -1 = A006134(p)-1. - _Benoit Cloitre_, Feb 08 2003
%C A003627 A039701(A049084(a(n))) = 2; A134323(A049084(a(n))) = -1. - _Reinhard Zumkeller_, Oct 21 2007
%C A003627 The set of primes of the form 3n - 1 is a superset of the set of lesser of twin primes larger than three (A001359). - _Paul Muljadi_, Jun 05 2008
%C A003627 Primes of this form do not occur in or as divisors of {n^2+n+1}. See A002383 (n^2+n+1 = prime), A162471 (prime divisors of n^2+n+1 not in A002383), and A002061 (numbers of the form n^2-n+1). - _Daniel Tisdale_, Jul 04 2009
%C A003627 Or, primes not in A007645. A003627 UNION A007645 = A000040. Also, primes of the form 6*k-5/2-+3/2. - _Juri-Stepan Gerasimov_, Jan 28 2010
%C A003627 Except for first term "2", all these prime numbers are of the form: 6*n-1. - _Vladimir Joseph Stephan Orlovsky_, Jul 13 2011
%C A003627 A088534(a(n)) = 0. - _Reinhard Zumkeller_, Oct 30 2011
%C A003627 For n>1: Numbers k such that (k-4)! mod k =(-1)^(floor(k/3)+1)*floor((k+1)/6), k>4. - _Gary Detlefs_, Jan 02 2012
%C A003627 Binomial(a(n),3)/a(n)= (3*A024893(n)^2+A024893(n))/2, n>1. - _Gary Detlefs_, May 06 2012
%C A003627 For every prime p in this sequence, 3 is a 9th power mod p. See Williams link. - _Michel Marcus_, Nov 12 2017
%C A003627 2 adjoined to A007528. - _David A. Corneth_, Nov 12 2017
%C A003627 For n >= 2 there exists a polygonal number P_s(3) = 3s - 3 = a(n) + 1. These are the only primes p with P_s(k) = p + 1, s >= 3, k >= 3, since P_s(k) - 1 is composite for k > 3. - _Ralf Steiner_, May 17 2018
%D A003627 M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 870.
%D A003627 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003627 T. D. Noe, <a href="/A003627/b003627.txt">Table of n, a(n) for n = 1..1000</a>
%H A003627 M. Abramowitz and I. A. Stegun, eds., <a href="http://www.convertit.com/Go/ConvertIt/Reference/AMS55.ASP">Handbook of Mathematical Functions</a>, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
%H A003627 A. Granville and G. Martin, <a href="http://www.arXiv.org/abs/math.NT/0408319">Prime number races</a>, arXiv:math/0408319 [math.NT], 2004.
%H A003627 Ernest G. Hibbs, <a href="https://www.proquest.com/openview/4012f0286b785cd732c78eb0fc6fce80">Component Interactions of the Prime Numbers</a>, Ph. D. Thesis, Capitol Technology Univ. (2022), see p. 33.
%H A003627 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EisensteinPrime.html">Eisenstein Prime</a>
%H A003627 Kenneth S. Williams, <a href="http://www.mscand.dk/article/view/11555/9571">3 as a Ninth Power (mod p)</a>, Math. Scand., Vol 35 (1974), 309-317.
%H A003627 <a href="https://oeis.org/index/Pri#primes_decomp_of">Index to sequences related to decomposition of primes in quadratic fields</a>
%F A003627 From _R. J. Mathar_, Apr 03 2011: (Start)
%F A003627 Sum_{n>=1} 1/a(n)^2 = 0.30792... = A085548 - 1/9 - A175644.
%F A003627 Sum_{n>=1} 1/a(n)^3 = 0.134125... = A085541 - 1/27 - A175645. (End)
%p A003627 t1 := {}; for n from 0 to 500 do if isprime(3*n+2) then t1 := {op(t1),3*n+2}; fi; od: A003627 := convert(t1,list);
%t A003627 Select[Range[-1, 600, 3], PrimeQ[#] &] (* _Vincenzo Librandi_, Jun 17 2015 *)
%t A003627 Select[Prime[Range[200]],Mod[#,3]==2&] (* _Harvey P. Dale_, Jan 31 2023 *)
%o A003627 (Magma) [n: n in PrimesUpTo(720) | n mod 3 eq 2]; // _Bruno Berselli_, Apr 05 2011
%o A003627 (Haskell)
%o A003627 a003627 n = a003627_list !! (n-1)
%o A003627 a003627_list = filter ((== 2) . (`mod` 3)) a000040_list
%o A003627 -- _Reinhard Zumkeller_, Oct 30 2011
%o A003627 (PARI) is(n)=n%3==2 && isprime(n) \\ _Charles R Greathouse IV_, Mar 20 2013
%Y A003627 Primes of form 3n+1 give A002476.
%Y A003627 These are the primes arising in A024893, A087370, A088879. A091177 gives prime index.
%Y A003627 Cf. A001359, A007528, A007645, A221717, A057145.
%Y A003627 Subsequence of A034020.
%K A003627 nonn,easy
%O A003627 1,1
%A A003627 _N. J. A. Sloane_ and _Mira Bernstein_