%I #25 Jul 14 2019 14:03:42

%S 7,103,127,223,367,463,487,607,727,823,967,1063,1087,1303,1327,1423,

%T 1447,1543,1567,1663,1783,2143,2287,2383,2503,2647,2767,2887,3343,

%U 3463,3583,3607,3727,3823,3847,3943,3967,4327,4423,4447,4567,4663

%N Primes of the form 7x^2+4xy+52y^2.

%C Discriminant=-1440. Also primes of the forms 7x^2+6xy+87y^2 and 7x^2+2xy+103y^2.

%C Voight proves that there are exactly 69 equivalence classes of positive definite binary quadratic forms that represent almost the same primes. 48 of those quadratic forms are of the idoneal type discussed in A139827. The remaining 21 begin at A140613 and end here. The cross-references section lists the quadratic forms in the same order as tables 1-6 in Voight's paper. Note that A107169 and A139831 are in the same equivalence class.

%C In base 12, the sequence is 7, 87, X7, 167, 267, 327, 347, 427, 507, 587, 687, 747, 767, 907, 927, 9X7, X07, X87, XX7, E67, 1047, 12X7, 13X7, 1467, 1547, 1647, 1727, 1807, 1E27, 2007, 20X7, 2107, 21X7, 2267, 2287, 2347, 2367, 2607, 2687, 26X7, 2787, 2847, where X is for 10 and E is for 11. Moreover, the discriminant is X00 and that all elements are {7, 87, X7, 167, 187, 247} mod 260. - _Walter Kehowski_, May 31 2008

%H Vincenzo Librandi and Ray Chandler, <a href="/A140633/b140633.txt">Table of n, a(n) for n = 1..10000</a> [First 1000 terms from Vincenzo Librandi]

%H N. J. A. Sloane et al., <a href="https://oeis.org/wiki/Binary_Quadratic_Forms_and_OEIS">Binary Quadratic Forms and OEIS</a> (Index to related sequences, programs, references)

%H John Voight, <a href="http://arXiv.org/abs/math.NT/0410266">Quadratic forms that represent almost the same primes</a>, Math. Comp., Vol. 76 (2007), pp. 1589-1617.

%t Union[QuadPrimes2[7, 4, 52, 10000], QuadPrimes2[7, -4, 52, 10000]] (* see A106856 *)

%Y Cf. A033205, A007519, A068228, A107135, A107144, A107152, A107151.

%Y Cf. A107181, A139502, A139856, A139854, A139874, A139877, A139897.

%Y Cf. A140613, A140614. A140615, A139923, A140616-A140619, A139988.

%Y Cf. A139993, A140008, A140010, A140620-A140632, A033212, A102273.

%Y Cf. A107007, A107003, A139830, A107169, A139831, A141373, A139847.

%Y Cf. A139850, A139855, A139860, A139879, A139880, A139924, A139990.

%Y Cf. A139998, A139992, A139996, A140003, A140013, A107006, A139858.

%Y Cf. A107008, A140633, A139991, A139857, A139859, A139878, A007645, A002313.

%K nonn,easy

%O 1,1

%A _T. D. Noe_, May 19 2008