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 A140505 #3 Mar 30 2012 18:51:58 %S A140505 2,-1,4,0,12,4,44,20,172,84,684,340,2732,1364,10924,5460,43692,21844, %T A140505 174764,87380,699052,349524,2796204,1398100,11184812,5592404,44739244, %U A140505 22369620,178956972,89478484,715827884,357913940,2863311532,1431655764,11453246124 %N A140505 Second differences of Jacobsthal sequence A001045, pairs with even and odd indices swapped. %C A140505 The second differences are -1, 2, 0, 4, 4, 12, 20, 44, ... (-1)^(n+1)*A084247(n), essentially A097073, which are listed here with -1 <=> 2, 0 <=> 4 etc. swapped in pairs. %F A140505 a(n) = 4*A092808(n-2), n>1. %F A140505 a(n+1) - 2a(n) = (-1)^n*A140504(n). %F A140505 O.g.f.: (2+x-5x^2)/[(1+x)(1-2x)(1+2x)]. - _R. J. Mathar_, Jul 08 2008 %K A140505 sign,less %O A140505 0,1 %A A140505 _Paul Curtz_, Jun 30 2008 %E A140505 Edited by _R. J. Mathar_, Jul 08 2008