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 A154890 #3 Mar 30 2012 18:52:00 %S A154890 3,6,4,8,8,16,24,48,88,176,344,688,1368,2736,5464,10928,21848,43696, %T A154890 87384,174768,349528,699056,1398104,2796208,5592408,11184816,22369624, %U A154890 44739248,89478488,178956976,357913944,715827888,1431655768,2863311536,5726623064 %N A154890 Jacobsthal numbers A001045 alternatingly incremented by 3 and 5. %F A154890 a(2n+1) = 2*a(2n). %F A154890 a(n) = A153643(n)+A010684(n). %F A154890 a(n+2) = 4*A128209(n). %F A154890 a(n) = 2*a(n-1)+a(n-2)-2*a(n-3). G.f.: (3-11x^2)/((1-x)(1+x)(1-2x)). [_R. J. Mathar_, Jan 23 2009] %K A154890 nonn,easy %O A154890 0,1 %A A154890 _Paul Curtz_, Jan 17 2009 %E A154890 Edited and extended by _R. J. Mathar_, Jan 23 2009