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 A129996 #7 Aug 25 2012 16:41:18 %S A129996 1,-1,-2,2,5,-5,-14,14,42,-42,-132,132,429,-429,-1430,1430,4862,-4862, %T A129996 -16796,16796,58786,-58786,-208012,208012,742900,-742900,-2674440, %U A129996 2674440,9694845,-9694845,-35357670,35357670,129644790,-129644790,-477638700,477638700 %N A129996 a(n) = (-1)^[(n+1)/2] A000108([n/2]+1). %C A129996 Terms of A000108(1,...) repeated, changing sign between the two repeated terms of same magnitude, but keeping the same sign for the next (larger) term. - _M. F. Hasler_, Aug 25 2012 %F A129996 First differences of A129110: a(n)=A129110(n+1)-A129110(n). %o A129996 (PARI) A129996(n)=(-1)^((n+1)\2)*A000108(n\2+1) \\ - _M. F. Hasler_, Aug 25 2012 %Y A129996 Cf. A099363, A106181 and A208355, which also consist of duplicated terms of A000108. - _M. F. Hasler_, Aug 25 2012 %K A129996 sign %O A129996 0,3 %A A129996 _Paul Curtz_, Jun 15 2007 %E A129996 Definition (formula) corrected by _M. F. Hasler_, Aug 25 2012