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 A086890 #5 Mar 30 2012 18:39:21 %S A086890 1,1,1,1,-1,-2,0,-10,29,-689,79779,-306741785,-537059115735445, %T A086890 32782820784889194174016393, %U A086890 123899509182081496572342154385115870319926534,6620488215208352146569523585853411114659592927465468100410366988520167986216 %N A086890 Imaginary part of Propp's cubic recurrence starting with i (i^2=-1). %C A086890 b(n)=x(n)+i*y(n) where x(n) and y(n) are integer sequences. %F A086890 a(n)=Im(b(n)) where b(1)=b(2)=b(3)=b(4)=i and b(n)=(1+b(n-1)*b(n-2)*b(n-3))/b(n-4) %Y A086890 Cf. A051786, A086889. %K A086890 sign %O A086890 1,6 %A A086890 _Benoit Cloitre_, Sep 17 2003