

A002145


Primes of the form 4n+3.
(Formerly M2624 N1039)


204



3, 7, 11, 19, 23, 31, 43, 47, 59, 67, 71, 79, 83, 103, 107, 127, 131, 139, 151, 163, 167, 179, 191, 199, 211, 223, 227, 239, 251, 263, 271, 283, 307, 311, 331, 347, 359, 367, 379, 383, 419, 431, 439, 443, 463, 467, 479, 487, 491, 499, 503, 523, 547, 563, 571
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS

Or, odd primes p such that 1 is not a square mod p, i.e., the Legendre symbol (1/p) = 1. [LeVeque I, p. 66].  N. J. A. Sloane, Jun 28 2008
Primes which are not the sum of two squares, see the comment in A022544.  Artur Jasinski, Nov 15 2006
Natural primes which are also Gaussian primes. (It is a common error to refer to this sequence as "the Gaussian primes".)
sin(a(n)*Pi/2) = 1 with Pi = 3.1415..., see A070750.  Reinhard Zumkeller, May 04 2002. (Misleading in the sense that the formula characterizes the supersequence A004767.  R. J. Mathar, Jul 28 2014)
Numbers n such that the product of coefficients of (2n)th cyclotomic polynomial equals 1.  Benoit Cloitre, Oct 22 2002
For p and q both belonging to the sequence, exactly one of the congruences x^2 = p (mod q), x^2 = q (mod p) is solvable, according to Gauss reciprocity law.  Lekraj Beedassy, Jul 17 2003
Also primes p that divide L((p1)/2) or L((p+1)/2), where L(n) = A000032(n), the Lucas numbers. Union of A122869 and A122870.  Alexander Adamchuk, Sep 16 2006
Also odd primes p that divide ((p1)!! + 1) or ((p2)!! + 1).  Alexander Adamchuk, Nov 30 2006
Also odd primes p that divide ((p1)!!  1) or ((p2)!!  1).  Alexander Adamchuk, Apr 18 2007
This sequence is a proper subset of the set of the absolute values of negative fundamental discriminants (A003657).  Paul Muljadi, Mar 29 2008
Bernard FrÃ©nicle de Bessy discovered that such primes cannot be the hypotenuse of a Pythagorean triangle in opposition to primes of the form 4*n+1 (see A002144).  after Paul Curtz, Sep 10 2008
A079261(a(n)) = 1; complement of A145395.  Reinhard Zumkeller, Oct 12 2008
Subsequence of A007970.  Reinhard Zumkeller, Jun 18 2011
A151763(a(n)) = 1.
Primes p such that p XOR 2 = p  2. Brad Clardy, Oct 25 2011 (Misleading in the sense that this is a formula for the supersequence A004767.  R. J. Mathar, Jul 28 2014)
It appears that each term of A004767 is the mean of two terms of this subsequence of primes therein; cf. A245203.  M. F. Hasler, Jul 13 2014
Numbers n > 2 such that ((n2)!!)^2 == 1 (mod n).  Thomas Ordowski, Jul 24 2016
Odd numbers n > 1 such that ((n1)!!)^2 == 1 (mod n).  Thomas Ordowski, Jul 25 2016
Primes p such that (p2)!! == (p3)!! (mod p).  Thomas Ordowski, Jul 28 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.
G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 5th ed., Oxford Univ. Press, 1979, p. 219, th. 252.
W. J. LeVeque, Topics in Number Theory. AddisonWesley, Reading, MA, 2 vols., 1956, Vol. 1, p. 66.
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

T. D. Noe and Moshe Levin, 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].
D. Alpern, Gaussian primes
A. Granville and G. Martin, Prime number races, arXiv:math/0408319 [math.NT], 2004.
E. T. Ordman, Tables of the class number for negative prime discriminants, Deposited in Unpublished Mathematical Table file of Math. Comp. [Annotated scanned partial copy with notes]
H. J. Smith, Gaussian Primes
Eric Weisstein's World of Mathematics, Gaussian Prime
Eric Weisstein's World of Mathematics, "Gaussian Integer".
Wolfram Research, The Gauss Reciprocity Law
Index entries for Gaussian integers and primes


FORMULA

Remove from A000040 terms that are in A002313.
Intersection of A000040 and A004767.  Alonso del Arte, Apr 22 2014


MAPLE

A002145 := proc(n)
option remember;
if n = 1 then
3;
else
a := nextprime(procname(n1)) ;
while a mod 4 <> 3 do
a := nextprime(a) ;
end do;
return a;
end if;
end proc:
seq(A002145(n), n=1..20) ; # R. J. Mathar, Dec 08 2011


MATHEMATICA

Select[4Range[150]  1, PrimeQ] (* Alonso del Arte, Dec 19 2013 *)
Select[ Prime@ Range[2, 110], Length@ PowersRepresentations[#^2, 2, 2] == 1 &] (* or *)
Select[ Prime@ Range[2, 110], JacobiSymbol[1, #] == 1 &] (* Robert G. Wilson v, May 11 2014 *)


PROG

(PARI) forprime(p=2, 1e3, if(p%4==3, print1(p", "))) \\ Charles R Greathouse IV, Jun 10 2011
(Haskell)
a002145 n = a002145_list !! (n1)
a002145_list = filter ((== 1) . a010051) [3, 7 ..]
 Reinhard Zumkeller, Aug 02 2015, Sep 23 2011
(MAGMA) [4*n+3 : n in [0..142]  IsPrime(4*n+3)]; // Arkadiusz Wesolowski, Nov 15 2013
(Sage)
A002145_list = lambda n: filter(lambda p: p % 4 == 3, list(primes(1, n))) # Peter Luschny, Jul 29 2014


CROSSREFS

Cf. A000032, A002144, A003657, A122869, A122870. Apart from initial term, same as A045326.
Cf. A016105.
Cf. A004614 (multiplicative closure).
Sequence in context: A080978 A160216 A181516 * A002052 A092109 A117991
Adjacent sequences: A002142 A002143 A002144 * A002146 A002147 A002148


KEYWORD

nonn,easy,changed


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from James A. Sellers, Apr 21 2000


STATUS

approved



