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 A155669 #11 Jun 12 2015 15:26:55 %S A155669 1,18,180,1728,16560,159048,1531440,14782968,143046720,1387420488, %T A155669 13486784400,131381059608,1282429536480,12541865828328, %U A155669 122876792454960,1205891132094648,11853020188851840,116677181699666568 %N A155669 10^n+9^n-1. %H A155669 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (20,-109,90). %F A155669 G.f.: 1/(1-10*x)+1/(1-9*x)-1/(1-x). E.g.f.: e^(10*x)+e^(9*x)-e^x. %F A155669 a(n)=19*a(n-1)-90*a(n-2)-72 with a(0)=1, a(1)=18 - _Vincenzo Librandi_, Jul 21 2010 %o A155669 (PARI) a(n)=10^n+9^n-1 \\ _Charles R Greathouse IV_, Jun 11 2015 %Y A155669 Cf. A155646, A155647, A155648, A155649, A155650, A155651, A155652, A155653, A155654, A155655, A155656, A155657, A155658, A155659, A155660, A155661, A155662, A155663, A155664, A155665, A155666, A155667, A155668. %K A155669 nonn,easy %O A155669 0,2 %A A155669 _Mohammad K. Azarian_, Feb 01 2009