The decimal expansion of 1/7 is 0.142857142857 …, a repeating decimal. Arrange the six repeating digits into overlapping ordered pairs, like so:
(1, 4), (4, 2), (2, 8), (8, 5), (5, 7) (7, 1),
and, remarkably, all six lie on an ellipse:
19x2 + 36yx + 41y2 – 333x – 531y + 1638 = 0
Even more remarkably, if we take the digits two at a time:
(14, 28), (42, 85), (28, 57), (85, 71), (57, 14), (71, 42),
these points also lie on an ellipse:
-165104x2 + 160804yx + 8385498x – 41651y2 – 3836349y – 7999600 = 0
That’s from David Wells, The Penguin Dictionary of Curious and Interesting Numbers (1986). Victor Hugo wrote, “Mankind is not a circle with a single center but an ellipse with two focal points, of which facts are one and ideas the other.”