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 A147675 #25 Feb 02 2024 11:02:48
%S A147675 10,5,20,10,40,20,80,40,160,80,320,160,640,320,1280,640,2560,1280,
%T A147675 5120,2560,10240,5120,20480,10240,40960,20480,81920,40960,163840,
%U A147675 81920,327680,163840,655360,327680,1310720,655360,2621440,1310720,5242880
%N A147675 Divide by 2, multiply by 4, repeat.
%C A147675 A147675-A147678 are from a quiz that someone asked me to help them with.
%H A147675 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,2).
%F A147675 From _R. J. Mathar_, Apr 22 2009: (Start)
%F A147675 a(n) = 2*a(n-2) = 5*A135530(n-1).
%F A147675 G.f.: 5*x*(2+x)/(1-2*x^2). (End)
%F A147675 From _Amiram Eldar_, Feb 02 2024: (Start)
%F A147675 Sum_{n>=1} 1/a(n) = 3/5.
%F A147675 Sum_{n>=1} (-1)^n/a(n) = 1/5. (End)
%t A147675 LinearRecurrence[{0, 2}, {10, 5}, 50] (* _Paolo Xausa_, Jan 30 2024 *)
%Y A147675 Cf. A020714, A135530.
%K A147675 nonn,easy
%O A147675 1,1
%A A147675 _N. J. A. Sloane_, Apr 21 2009
%E A147675 More terms from _R. J. Mathar_, Apr 22 2009