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 A087785 #3 Mar 31 2012 13:20:50 %S A087785 1,4,6,12,32,24,42,48,54,128,110,72,184,168,192,192,308,216,342,384, %T A087785 252,440,506,288,752,736,486,504,872,768,930,768,660,1232,1344,648, %U A087785 1408,1368,1104,1536,1724,1008,1806,1320,1728,2024,2162,1152,2058,3008,1848 %N A087785 Number of elements in GL(2,Z_n) x with x^2 == -I mod n where I is the identity matrix. %Y A087785 Cf. A066907, A000089. %K A087785 mult,nonn %O A087785 1,2 %A A087785 Yuval Dekel (dekelyuval(AT)hotmail.com), Oct 06 2003 %E A087785 More terms from _David Wasserman_, Jun 17 2005