%N Calendar Problem #27, April 2012 Mathematics Teacher.
%C The numbers are paired on the basis of rotational symmetry with alternating signs.
%H 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 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 Cf. A045574, A054047.
%A _Jonathan Vos Post_, Mar 01 2012