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 A155588 #28 Mar 10 2022 05:35:00
%S A155588 1,6,28,132,640,3156,15688,78252,390880,1953636,9766648,48830172,
%T A155588 244144720,1220711316,6103532008,30517610892,152587956160,
%U A155588 762939584196,3814697527768,19073486852412,95367432689200,476837160300276
%N A155588 a(n) = 5^n + 2^n - 1^n.
%H A155588 Michael De Vlieger, <a href="/A155588/b155588.txt">Table of n, a(n) for n = 0..1430</a>
%H A155588 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (8,-17,10).
%F A155588 G.f.: 1/(1-5*x)+1/(1-2*x)-1/(1-x).
%F A155588 E.g.f.: e^(5*x)+e^(2*x)-e^x.
%F A155588 a(n) = 7*a(n-1)-10*a(n-2)-4 with a(0)=1, a(1)=6. - _Vincenzo Librandi_, Jul 21 2010
%F A155588 a(n) = A074600(n)-1. - _R. J. Mathar_, Mar 10 2022
%t A155588 CoefficientList[Series[1/(1 - 5 x) + 1/(1 - 2 x) - 1/(1 - x), {x, 0, 21}], x] (* _Michael De Vlieger_, Mar 02 2022 *)
%o A155588 (PARI) a(n)=5^n+2^n-1 \\ _Charles R Greathouse IV_, Sep 24 2015
%Y A155588 Cf. A074501, A074600, A005057, A005056, A099393.
%K A155588 nonn,easy
%O A155588 0,2
%A A155588 _Mohammad K. Azarian_, Jan 24 2009