

A002476


Primes of the form 6m + 1.
(Formerly M4344 N1819)


195



7, 13, 19, 31, 37, 43, 61, 67, 73, 79, 97, 103, 109, 127, 139, 151, 157, 163, 181, 193, 199, 211, 223, 229, 241, 271, 277, 283, 307, 313, 331, 337, 349, 367, 373, 379, 397, 409, 421, 433, 439, 457, 463, 487, 499, 523, 541, 547, 571, 577, 601, 607, 613, 619
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OFFSET

1,1


COMMENTS

Equivalently, primes of the form 3m + 1.
Rational primes that decompose in the field Q(sqrt(3)).  N. J. A. Sloane, Dec 25 2017
Primes p dividing Sum_{k=0..p} binomial(2k, k)  3 = A006134(p)  3.  Benoit Cloitre, Feb 08 2003
Primes p such that tau(p) == 2 (mod 3) where tau(x) is the Ramanujan tau function (cf. A000594).  Benoit Cloitre, May 04 2003
Primes of the form x^2 + xy  2y^2 = (x+2y)(xy).  N. J. A. Sloane, May 31 2014
Primes of the form x^2  xy + 7y^2 with x and y nonnegative.  T. D. Noe, May 07 2005
Primes p such that p^2 divides Sum_{m=1..2(p1)} Sum_{k=1..m} (2k)!/(k!)^2.  Alexander Adamchuk, Jul 04 2006
A006512 larger than 5 (Greater of twin primes) is a subset of this.  Jonathan Vos Post, Sep 03 2006
A039701(A049084(a(n))) = A134323(A049084(a(n))) = 1.  Reinhard Zumkeller, Oct 21 2007
Also primes p such that the arithmetic mean of divisors of p^2 is an integer: sigma_1(p^2)/sigma_0(p^2) = C. (A000203(p^2)/A000005(p^2) = C).  Ctibor O. Zizka, Sep 15 2008
Fermat knew that these numbers can also be expressed as x^2 + 3y^2 and are therefore not prime in Z[omega], where omega is a complex cubic root of unity.  Alonso del Arte, Dec 07 2012
Primes of the form x^2 + xy + y^2 with x < y and nonnegative. Also see A007645 which also applies when x=y, adding an initial 3.  Richard R. Forberg, Apr 11 2016
For any term p in this sequence, let k = (p^2  1)/6; then A016921(k) = p^2.  Sergey Pavlov, Dec 16 2016; corrected Dec 18 2016


REFERENCES

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.
David A. Cox, Primes of the Form x^2 + ny^2. New York: Wiley (1989): 8.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Ray Chandler, Table of n, a(n) for n = 1..10000 (first 1000 terms from T. D. Noe)
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
C. Banderier, Calcul de (3/p)
F. S. Carey, On some cases of the Solutions of the Congruence z^p^(n1)=1, mod p, Proceedings of the London Mathematical Society, Volume s133, Issue 1, November 1900, Pages 294312.
A. Granville and G. Martin, Prime number races, arXiv:math/0408319 [math.NT], 2004.
K. G. Reuschle, Tafeln complexer Primzahlen, Königl. Akademie der Wissenschaften, Berlin, 1875, p. 1.
Neville Robbins, On the Infinitude of Primes of the Form 3k+1, Fib. Q., 43,1 (2005), 2930.
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)
Index to sequences related to decomposition of primes in quadratic fields


FORMULA

From R. J. Mathar, Apr 03 2011: (Start)
Sum_{n >= 1} 1/a(n)^2 = A175644.
Sum_{n >= 1} 1/a(n)^3 = A175645. (End)
a(n) = 6*A024899(n) + 1.  Zak Seidov, Aug 31 2016
From Vaclav Kotesovec, May 02 2020: (Start)
Product_{k>=1} (1  1/a(k)^2) = 1/A175646.
Product_{k>=1} (1 + 1/a(k)^2) = A334481.
Product_{k>=1} (1  1/a(k)^3) = A334478.
Product_{k>=1} (1 + 1/a(k)^3) = A334477. (End)


EXAMPLE

Since 6 * 1 + 1 = 7 and 7 is prime, 7 is in the sequence. (Also 7 = 2^2 + 3 * 1^2 = (2 + sqrt(3))(2  sqrt(3)).)
Since 6 * 2 + 1 = 13 and 13 is prime, 13 is in the sequence.
17 is prime but it is of the form 6m  1 rather than 6m + 1, and is therefore not in the sequence.


MAPLE

a := [ ]: for n from 1 to 400 do if isprime(6*n+1) then a := [ op(a), n ]; fi; od: A002476 := n>a[n];


MATHEMATICA

Select[6*Range[100] + 1, PrimeQ[ # ] &] (* Stefan Steinerberger, Apr 06 2006 *)


PROG

(MAGMA) [n: n in [1..700 by 6]  IsPrime(n)]; // Vincenzo Librandi, Apr 05 2011
(PARI) select(p>p%3==1, primes(100)) \\ Charles R Greathouse IV, Oct 31 2012
(Haskell)
a002476 n = a002476_list !! (n1)
a002476_list = filter ((== 1) . (`mod` 6)) a000040_list
 Reinhard Zumkeller, Jan 15 2013
(J) (#~ 1&p:) >: 6 * i.1000 NB. Stephen Makdisi, May 01 2018
(GAP) Filtered(List([0..110], k>6*k+1), n> IsPrime(n)); # Muniru A Asiru, Mar 11 2019


CROSSREFS

Cf. A045331, A242660.
For values of m see A024899. Primes of form 3n  1 give A003627.
These are the primes arising in A024892, A024899, A034936.
A091178 gives prime index.
Cf. A006512.
Subsequence of A016921 and of A050931.
Cf. A004611 (multiplicative closure).
Sequence in context: A218146 A129389 A107925 * A123365 A144921 A272409
Adjacent sequences: A002473 A002474 A002475 * A002477 A002478 A002479


KEYWORD

nonn,nice,easy


AUTHOR

N. J. A. Sloane


STATUS

approved



