A257414 Values of n such that there are exactly 7 solutions to x^2 - y^2 = n with x > y >= 0.

768, 1280, 1792, 2816, 3328, 3645, 4352, 4864, 5103, 5832, 5888, 7424, 7936, 8019, 9472, 9477, 10496, 11008, 12032, 12393, 13568, 13851, 14580, 15104, 15616, 16384, 16767, 17152, 18176, 18688, 20224, 20412, 21141, 21248, 22599, 22784, 24832, 25856, 26368

Offset: 1

Author

Colin Barker, Apr 22 2015

Keywords

• nonn

Examples

			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).
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..10000 (first 120 terms from Colin Barker)

Crossrefs

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

Cf. A034178, A068314.

Programs

Mathematica

nn = 30000;
t = Table[0, {nn}];
Do[n = x^2 - y^2; If[n <= nn, t[[n]]++], {x, nn}, {y, 0, x - 1}];
Position[t, 7] // Flatten (* Jean-François Alcover, Jun 18 2020, after T. D. Noe in A034178 *)

PARI

is_A257414(n)={A034178(n)==7} \\ M. F. Hasler, Apr 22 2015