A257414 - OEIS

A257414

Values of n such that there are exactly 7 solutions to x^2 - y^2 = n with x > y >= 0.

%I #19 Jun 18 2020 16:32:09

%S 768,1280,1792,2816,3328,3645,4352,4864,5103,5832,5888,7424,7936,8019,

%T 9472,9477,10496,11008,12032,12393,13568,13851,14580,15104,15616,

%U 16384,16767,17152,18176,18688,20224,20412,21141,21248,22599,22784,24832,25856,26368

%N Values of n such that there are exactly 7 solutions to x^2 - y^2 = n with x > y >= 0.

%H David A. Corneth, <a href="/A257414/b257414.txt">Table of n, a(n) for n = 1..10000</a> (first 120 terms from Colin Barker)

%e 768 is in the sequence because there are 7 solutions to x^2 - y^2 = 768, namely (x,y) = (28,4), (32,16), (38,26), (52,44), (67,61), (98,94), (193,191).

%t nn = 30000;

%t t = Table[0, {nn}];

%t Do[n = x^2 - y^2; If[n <= nn, t[[n]]++], {x, nn}, {y, 0, x - 1}];

%t Position[t, 7] // Flatten (* _Jean-François Alcover_, Jun 18 2020, after _T. D. Noe_ in A034178 *)

%o (PARI) is_A257414(n)={A034178(n)==7} \\ _M. F. Hasler_, Apr 22 2015

%Y Cf. A257408, A257409, A257410, A257411, A257412, A257413, A257415, A257416, A257417.

%Y Cf. A034178, A068314.

%K nonn

%O 1,1

%A _Colin Barker_, Apr 22 2015