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 A257413 Values of n such that there are exactly 6 solutions to x^2 - y^2 = n with x > y >= 0. 8
 240, 288, 315, 336, 360, 384, 432, 495, 504, 525, 528, 560, 585, 600, 624, 640, 675, 693, 735, 765, 792, 800, 816, 819, 825, 855, 880, 896, 912, 936, 975, 1035, 1040, 1071, 1104, 1125, 1176, 1197, 1215, 1224, 1232, 1260, 1275, 1287, 1305, 1323, 1360, 1368 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Colin Barker, Table of n, a(n) for n = 1..1100 EXAMPLE 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). MATHEMATICA nn = 2000; t = Table[0, {nn}]; Do[n = x^2 - y^2; If[n <= nn, t[[n]]++], {x, nn}, {y, 0, x - 1}]; Position[t, 6] // Flatten (* Jean-François Alcover, Jun 18 2020, after T. D. Noe in A034178 *) PROG (PARI) is_A257413(n)={A034178(n)==6} \\ M. F. Hasler, Apr 22 2015 CROSSREFS Cf. A257408, A257409, A257410, A257411, A257412, A257414, A257415, A257416, A257417. Cf. A034178. Sequence in context: A031173 A067373 A291921 * A030638 A179644 A099833 Adjacent sequences:  A257410 A257411 A257412 * A257414 A257415 A257416 KEYWORD nonn AUTHOR Colin Barker, Apr 22 2015 STATUS approved

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Last modified November 27 18:22 EST 2020. Contains 338683 sequences. (Running on oeis4.)