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 A081660 #17 Feb 23 2025 16:44:32
%S A081660 1,2,5,8,15,26,49,92,179,350,693,1376,2743,5474,10937,21860,43707,
%T A081660 87398,174781,349544,699071,1398122,2796225,5592428,11184835,22369646,
%U A081660 44739269,89478512,178956999,357913970,715827913,1431655796,2863311563
%N A081660 n+A001045(n+1).
%H A081660 Vincenzo Librandi, <a href="/A081660/b081660.txt">Table of n, a(n) for n = 0..1000</a>
%H A081660 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,-1,-3,2)
%F A081660 a(n) = 2^(n+1)/3+n+(-1)^n/3.
%F A081660 G.f.: (1-x-2*x^3)/((1+x)*(1-2*x)*(1-x)^2). [_Bruno Berselli_, Aug 11 2013]
%t A081660 Table[2^(n + 1)/3 + n + (-1)^n/3, {n, 0, 40}] (* _Vincenzo Librandi_, Aug 10 2013 *)
%t A081660 LinearRecurrence[{3,-1,-3,2},{1,2,5,8},40] (* _Harvey P. Dale_, Feb 23 2025 *)
%o A081660 (Magma) [2^(n+1)/3+n+(-1)^n/3: n in [0..40]]; // _Vincenzo Librandi_, Aug 10 2013
%Y A081660 Cf. A001045, A081659.
%K A081660 nonn,easy
%O A081660 0,2
%A A081660 _Paul Barry_, Mar 26 2003