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 A155623 #17 Sep 03 2018 04:20:52
%S A155623 1,13,129,1357,14721,161293,1772289,19489357,214365441,2357967373,
%T A155623 25937483649,285311847757,3138428908161,34522713738253,
%U A155623 379749838366209,4177248183764557,45949729906618881,505447028628433933
%N A155623 a(n) = 11^n + 3^n - 1.
%C A155623 a^n+b^n-1^n=(a+b)*a(n-1)-(a*b)*a(n-2)-(a-1)*(b-1) - _Vincenzo Librandi_, Jul 21 2010
%H A155623 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (15,-47,33).
%F A155623 G.f.: 1/(1 - 11*x) + 1/(1 - 3*x) - 1/(1 - x).
%F A155623 E.g.f.: exp(11*x) + exp(3*x) - exp(x).
%F A155623 a(n) = 14*a(n-1) - 33*a(n-2) - 20 for n>1, a(0)=1, a(1)=13 - _Vincenzo Librandi_, Jul 21 2010
%t A155623 LinearRecurrence[{15,-47,33},{1,13,129},20] (* _Harvey P. Dale_, Jan 14 2015 *)
%o A155623 (PARI) a(n)=11^n+3^n-1 \\ _Charles R Greathouse IV_, Jun 11 2015
%Y A155623 Cf. A155588, A155589, A155590, A155592, A155593, A155594, A155595, A155596, A155597, A155598, A155599, A155600, A155601, A155622.
%K A155623 nonn,easy
%O A155623 0,2
%A A155623 _Mohammad K. Azarian_, Jan 29 2009