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 A140721 #3 Mar 30 2012 18:51:58 %S A140721 1,-7,4,-28,16,-112,64,-448,256,-1792,1024,-7168,4096,-28672,16384, %T A140721 -114688,65536,-458752,262144,-1835008,1048576,-7340032,4194304, %U A140721 -29360128,16777216,-117440512,67108864,-469762048,268435456,-1879048192,1073741824 %N A140721 Alternated reading of A000302 and negated A002042. %C A140721 Sequence can also be obtained by negating the first differences of A135520: a(n)=A135520(n)-A135520(n+1). %F A140721 a(2n) = A000302(n). a(2n+1) = -A002042(n) . %F A140721 a(2n) = -7a(2n-1). a(2n)-a(2n-1) = A002089(n-1). a(n)+a(n+1) = -3*A135520(n). %F A140721 O.g.f.: (7x-1)/((2x-1)(2x+1)). - _R. J. Mathar_, Jul 14 2008 %K A140721 sign,less %O A140721 0,2 %A A140721 _Paul Curtz_, Jul 12 2008 %E A140721 Edited by _R. J. Mathar_, Jul 14 2008