A257412 Values of n such that there are exactly 5 solutions to x^2 - y^2 = n with x > y >= 0.

144, 192, 225, 320, 400, 405, 441, 448, 567, 648, 704, 784, 832, 891, 900, 1024, 1053, 1088, 1089, 1216, 1225, 1377, 1472, 1521, 1539, 1620, 1764, 1856, 1863, 1875, 1936, 1984, 2048, 2268, 2349, 2368, 2511, 2601, 2624, 2704, 2752, 2997, 3008, 3025, 3249

Offset

1,1

Links

David A. Corneth, Table of n, a(n) for n = 1..10000 (first 150 terms from Colin Barker)

Example

144 is in the sequence because there are 5 solutions to x^2 - y^2 = 144, namely (x,y) = (12,0), (13,5), (15,9), (20,16), (37,35).

Mathematica

nn = 4000;
t = Table[0, {nn}];
Do[n = x^2 - y^2; If[n <= nn, t[[n]]++], {x, nn}, {y, 0, x - 1}];
Position[t, 5] // Flatten (* Jean-François Alcover, Jun 18 2020, after T. D. Noe in A034178 *)

Prog

(PARI) is_A257412(n)={A034178(n)==5} \\ M. F. Hasler, Apr 22 2015

Crossrefs

Cf. A257408, A257409, A257410, A257411, A257413, A257414, A257415, A257416, A257417.

Cf. A034178.

Sequence in context: A156316 A323614 A245214 * A165076 A165078 A135780

Adjacent sequences: A257409 A257410 A257411 * A257413 A257414 A257415

Keyword

nonn

Author

Colin Barker, Apr 22 2015

Status

approved