A106881 -id:A106881 - cp's OEIS frontend

A106856 Primes of the form x^2 + xy + 2y^2, with x and y nonnegative.

2, 11, 23, 37, 43, 53, 71, 79, 107, 109, 127, 137, 149, 151, 163, 193, 197, 211, 233, 239, 263, 281, 317, 331, 337, 373, 389, 401, 421, 431, 443, 463, 487, 491, 499, 541, 547, 557, 569, 599, 613, 617, 641, 653, 659, 673, 683, 739, 743, 751, 757, 809, 821

Offset: 1

T. D. Noe, May 09 2005, Apr 28 2008

Discriminant=-7. Binary quadratic forms ax^2 + bxy + cy^2 have discriminant d = b^2 - 4ac.

Consider sequences of primes produced by forms with -100

The Mathematica function QuadPrimes2 is useful for finding the primes less than "lim" represented by the positive definite quadratic form ax^2 + bxy + cy^2 for any a, b and c satisfying a>0, c>0, and discriminant d<0. It does this by examining all x>=0 and y>=0 in the ellipse ax^2 + bxy + cy^2 <= lim. To find the primes generated by positive and negative x and y, compute the union of QuadPrimes2[a,b,c,lim] and QuadPrimes2[a,-b,c,lim]. - T. D. Noe, Sep 01 2009

For other programs see the "Binary Quadratic Forms and OEIS" link.

David A. Cox, Primes of the Form x^2 + n y^2, Wiley, 1989.
L. E. Dickson, History of the Theory of Numbers, Vol. 3, Chelsea, 1923.

Zak Seidov and N. J. A. Sloane, Table of n, a(n) for n = 1..10000 (The first 1225 terms were found by Zak Seidov)
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Discriminants in the range -3 to -100: A007645 (d=-3), A002313 (d=-4), A045373, A106856 (d=-7), A033203 (d=-8), A056874, A106857 (d=-11), A002476 (d=-12), A033212, A106858-A106861 (d=-15), A002144, A002313 (d=-16), A106862-A106863 (d=-19), A033205, A106864-A106865 (d=-20), A106866-A106869 (d=-23), A033199, A084865 (d=-24), A002476, A106870 (d=-27), A033207 (d=-28), A033221, A106871-A106874 (d=-31), A007519, A007520, A106875-A106876 (d=-32), A106877-A106881 (d=-35), A040117, A068228, A106882 (d=-36), A033227, A106883-A106888 (d=-39), A033201, A106889 (d=-40), A106890-A106891 (d=-43), A033209, A106282, A106892-A106893 (d=-44), A033232, A106894-A106900 (d=-47), A068229 (d=-48), A106901-A106904 (d=-51), A033210, A106905-A106906 (d=-52), A033235, A106907-A106913 (d=-55), A033211, A106914-A106917 (d=-56), A106918-A106922 (d=-59), A033212, A106859 (d=-60), A106923-A106930 (d=-63), A007521, A106931 (d=-64), A106932-A106933 (d=-67), A033213, A106934-A106938 (d=-68), A033246, A106939-A106948 (d=-71), A106949-A106950 (d=-72), A033212, A106951-A106952 (d=-75), A033214, A106953-A106955 (d=-76), A033251, A106956-A106962 (d=-79), A047650, A106963-A106965 (d=-80), A106966-A106970 (d=-83), A033215, A102271, A102273, A106971-A106974 (d=-84), A033256, A106975-A106983 (d=-87), A033216, A106984 (d=-88), A106985-A106989 (d=-91), A033217 (d=-92), A033206, A106990-A107001 (d=-95), A107002-A107008 (d=-96), A107009-A107013 (d=-99).
Other collections of quadratic forms: A139643, A139827.
For a more comprehensive list of sequences giving numbers and/or primes represented by binary quadratic forms, see the "Binary Quadratic Forms and OEIS" link.
Cf. also A242660.

QuadPrimes2[a_, b_, c_, lmt_] := Module[{p, d, lst = {}, xMax, yMax}, d = b^2 - 4a*c; If[a > 0 && c > 0 && d < 0, xMax = Sqrt[lmt/a]*(1+Abs[b]/Floor[Sqrt[-d]])]; Do[ If[ 4c*lmt + d*x^2 >= 0, yMax = ((-b)*x + Sqrt[4c*lmt + d*x^2])/(2c), yMax = 0 ]; Do[p = a*x^2 + b*x*y + c*y^2; If[ PrimeQ[ p]  && p <= lmt && !MemberQ[ lst, p], AppendTo[ lst, p]], {y, 0, yMax}], {x, 0, xMax}]; Sort[ lst]];
QuadPrimes2[1, 1, 2, 1000]
(This is a corrected version of the old, incorrect, program QuadPrimes. - N. J. A. Sloane, Jun 15 2014)
max = 1000; Table[yy = {y, 1, Floor[Sqrt[8 max - 7 x^2]/4 - x/4]}; Table[ x^2 + x y + 2 y^2, yy // Evaluate], {x, 0, Floor[Sqrt[max]]}] // Flatten // Union // Select[#, PrimeQ]& (* Jean-François Alcover, Oct 04 2018 *)

list(lim)=my(q=Qfb(1,1,2), v=List([2])); forprime(p=2, lim, if(vecmin(qfbsolve(q, p))>0, listput(v,p))); Vec(v) \\ Charles R Greathouse IV, Aug 05 2016

Removed old Mathematica programs - T. D. Noe, Sep 09 2009

Edited (pointed out error in QuadPrimes, added new version of program, checked and extended b-file). - N. J. A. Sloane, Jun 06 2014

A191026 Primes p that have Jacobi symbol (p|35) = 1.

Original entry on oeis.org

3, 11, 13, 17, 29, 47, 71, 73, 79, 83, 97, 103, 109, 149, 151, 157, 167, 173, 179, 191, 211, 223, 227, 239, 257, 281, 283, 293, 307, 313, 331, 353, 359, 367, 379, 383, 389, 397, 401, 421, 431, 433, 449, 467, 491, 499, 503, 523, 541, 563, 569, 571, 577, 587

Offset: 1

T. D. Noe, May 24 2011

Originally incorrectly named "Primes which are squares (mod 35)", which is subsequence A106881. - M. F. Hasler, Jan 15 2016

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Cf. A191017, A191018, A191020, A191023, A191025.

[p: p in PrimesUpTo(587) | JacobiSymbol(p,35) eq 1]; // Vincenzo Librandi, Sep 10 2012

Select[Prime[Range[200]], JacobiSymbol[#,35]==1&]

is(p)=kronecker(p, 35)==1&&isprime(p) \\ M. F. Hasler, Jan 15 2016

Definition corrected (following an observation by David Broadhurst) by M. F. Hasler, Jan 15 2016

A191043 Primes p that have Kronecker symbol (p|70) = 1.

Original entry on oeis.org

17, 19, 37, 43, 47, 53, 59, 61, 67, 71, 73, 79, 97, 101, 103, 107, 131, 139, 151, 163, 167, 181, 191, 197, 223, 229, 239, 251, 257, 269, 277, 281, 313, 317, 347, 349, 353, 359, 367, 373, 383, 401, 419, 431, 433, 443, 449, 461, 503, 509, 547, 557, 569, 577

Offset: 1

T. D. Noe, May 25 2011

Originally incorrectly named "primes which are squares mod 70", which is sequence A106881. - M. F. Hasler, Jan 15 2016

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Cf. A191017, A191018, A191020, A191023, A191025, A191026, A191028, A191029, A191032, A191034, A191036, A191037, A191040, A191042.

[p: p in PrimesUpTo(577) | KroneckerSymbol(p, 70) eq 1]; // Vincenzo Librandi, Sep 11 2012

Select[Prime[Range[200]], JacobiSymbol[#,70]==1&]

select(p->kronecker(p, 70)==1&&isprime(p), [1..1000]) \\ This is to provide a generic characteristic function ("is_A191043") as 1st arg of select(), there are other ways to produce the sequence more efficiently. - M. F. Hasler, Jan 15 2016

Definition corrected (following an observation by David Broadhurst) by M. F. Hasler, Jan 15 2016

A267455 Primes which are a square (mod 39).

Original entry on oeis.org

3, 13, 43, 61, 79, 103, 127, 139, 157, 181, 199, 211, 277, 283, 313, 337, 367, 373, 433, 439, 523, 547, 571, 601, 607, 673, 727, 751, 757, 823, 829, 859, 883, 907, 919, 937, 991, 997, 1039, 1063, 1069, 1093, 1117, 1153, 1171, 1213, 1231, 1249, 1291, 1297, 1303, 1327, 1381, 1429, 1447, 1453, 1459, 1483

Offset: 1

M. F. Hasler, Jan 15 2016

Motivated by the former (incorrect) definition of A191029.
Also, primes p which have Legendre symbols (p|3) = (p|13) = 1, together with 3 and 13.
Apparently this contains the 3 plus the elements of A139494. - R. J. Mathar, May 28 2025

Paolo Xausa, Table of n, a(n) for n = 1..10000

Cf. A038889, A045373, A056874, A106863, A106881, A191029.

Cf. A139494.

Join[{3, 13}, Select[Prime[Range[500]], JacobiSymbol[#, {3, 13}] == {1, 1} &]] (* Paolo Xausa, May 29 2025 *)

select(p->issquare(Mod(p,39))&&isprime(p),[1..1000])

A106880 Primes of the form x^2+xy+9y^2, with x and y nonnegative.

Original entry on oeis.org

11, 29, 71, 109, 149, 151, 179, 191, 211, 239, 281, 331, 359, 379, 389, 401, 421, 449, 491, 499, 541, 571, 599, 631, 641, 659, 701, 739, 751, 809, 821, 911, 919, 991, 1009, 1019, 1031, 1051, 1129, 1171, 1201, 1229, 1289, 1381, 1409, 1429, 1439, 1451

Offset: 1

T. D. Noe, May 09 2005

Discriminant=-35.

Vincenzo Librandi and Ray Chandler, Table of n, a(n) for n = 1..10000 [First 1000 terms from Vincenzo Librandi]
N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Cf. A106881.

QuadPrimes2[1, 1, 9, 10000] (* see A106856 *)

A243178 Numbers of the form x^2+xy+9y^2.

Original entry on oeis.org

0, 1, 4, 9, 11, 15, 16, 21, 25, 29, 35, 36, 39, 44, 49, 51, 60, 64, 65, 71, 79, 81, 84, 85, 91, 99, 100, 109, 116, 119, 121, 135, 140, 141, 144, 149, 151, 156, 165, 169, 176, 179, 189, 191, 196, 204, 211, 219, 221, 225, 231, 235, 239, 240, 249, 256, 260, 261, 275, 281, 284, 289, 291, 309, 315, 316, 319, 324, 329, 331, 336, 340, 351, 359, 361, 364, 365, 375

Offset: 1

N. J. A. Sloane, Jun 02 2014

nonn

Discriminant -35.

N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references)

Primes: A106881.

ofTheFormQ[n_] := Reduce[n == x^2 + x*y + 9*y^2, {x, y}, Integers] =!= False; Select[Range[0, 400], ofTheFormQ] (* Jean-François Alcover, Jun 04 2014 *)

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A106856 Primes of the form x^2 + xy + 2y^2, with x and y nonnegative.

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A191026 Primes p that have Jacobi symbol (p|35) = 1.

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Magma

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A191043 Primes p that have Kronecker symbol (p|70) = 1.

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Magma

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A267455 Primes which are a square (mod 39).

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PARI

A106880 Primes of the form x^2+xy+9y^2, with x and y nonnegative.

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Mathematica

A243178 Numbers of the form x^2+xy+9y^2.

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Mathematica