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%I #14 Jun 18 2020 23:25:03
%S 240,288,315,336,360,384,432,495,504,525,528,560,585,600,624,640,675,
%T 693,735,765,792,800,816,819,825,855,880,896,912,936,975,1035,1040,
%U 1071,1104,1125,1176,1197,1215,1224,1232,1260,1275,1287,1305,1323,1360,1368
%N Values of n such that there are exactly 6 solutions to x^2 - y^2 = n with x > y >= 0.
%H Colin Barker, <a href="/A257413/b257413.txt">Table of n, a(n) for n = 1..1100</a>
%e 240 is in the sequence because there are 6 solutions to x^2 - y^2 = 240, namely (x,y) = (16,4), (17,7), (19,11), (23,17), (32,28), (61,59).
%t nn = 2000;
%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, 6] // Flatten (* _Jean-François Alcover_, Jun 18 2020, after _T. D. Noe_ in A034178 *)
%o (PARI) is_A257413(n)={A034178(n)==6} \\ _M. F. Hasler_, Apr 22 2015
%Y Cf. A257408, A257409, A257410, A257411, A257412, A257414, A257415, A257416, A257417.
%Y Cf. A034178.
%K nonn
%O 1,1
%A _Colin Barker_, Apr 22 2015
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