This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A208646 #12 Sep 01 2014 05:02:19 %S A208646 9861,-1986,9681,-1896,8961,-1968,8691,-1698 %N A208646 Calendar Problem #27, April 2012 Mathematics Teacher. %C A208646 The numbers are paired on the basis of rotational symmetry with alternating signs. %H A208646 Margaret Coffey, Editor, <a href="http://www.jstor.org/stable/10.5951/mathteacher.105.7.0520">Calendar Problem #27</a>, April 2012 Mathematics Teacher, pp. 521, 524. %e A208646 If you rotate the first number, 9861, 180 degrees about its center, and put a negative sign in front, you get the second number: -1986. Similarly, the third and fourth numbers are rotations of each other, as well as of the fifth and sixth numbers. Therefore the eighth number is the rotation and negation of the seventh number, 8961, which would be -1698. %Y A208646 Cf. A045574, A054047. %K A208646 sign,easy,base %O A208646 1,1 %A A208646 _Jonathan Vos Post_, Mar 01 2012