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 A220087 #17 Nov 08 2023 06:53:13
%S A220087 -26,-25,-23,-19,-11,5,37,101,229,485,997,2021,4069,8165,16357,32741,
%T A220087 65509,131045,262117,524261,1048549,2097125,4194277,8388581,16777189,
%U A220087 33554405,67108837,134217701,268435429,536870885,1073741797,2147483621,4294967269
%N A220087 a(n) = 2^n - 27.
%H A220087 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2).
%F A220087 From _Chai Wah Wu_, Jan 17 2020: (Start)
%F A220087 a(n) = 3*a(n-1) - 2*a(n-2) for n > 1.
%F A220087 G.f.: (53*x - 26)/((x - 1)*(2*x - 1)). (End)
%F A220087 From _Elmo R. Oliveira_, Nov 08 2023: (Start)
%F A220087 a(n) = 2*a(n-1) + 27 with a(0) = -26.
%F A220087 E.g.f.: exp(2*x) - 27*exp(x). (End)
%t A220087 Table[2^n - 27, {n, 0, 40}] (* _T. D. Noe_, Dec 04 2012 *)
%t A220087 LinearRecurrence[{3,-2},{-26,-25},40] (* _Harvey P. Dale_, May 17 2018 *)
%Y A220087 Cf. A000225, A036563, A185346.
%K A220087 sign
%O A220087 0,1
%A A220087 _Andreas Rieber_, Dec 04 2012