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 A155611 #14 Jun 13 2015 00:52:47 %S A155611 1,4,28,190,1216,7534,45928,277750,1673056,10058014,60407128, %T A155611 362619910,2176250896,13059099694,78359381128,470170635670, %U A155611 2821066860736,16926530304574,101559569247928,609358577749030,3656154953278576 %N A155611 6^n - 3^n + 1. %H A155611 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (10,-27,18). %F A155611 G.f.: 1/(1-6*x)-1/(1-3*x)+1/(1-x). E.g.f.: e^(6*x)-e^(3*x)+e^x. %F A155611 a(n)=9*a(n-1)-18*a(n-2)+10 with a(0)=1, a(1)=4 [From _Vincenzo Librandi_, Jul 21 2010] %F A155611 E.g.f.: exp(6*x)-exp(3*x)+exp(x)= G(0) ; G(k)= 1 - 1/( 2^k + 2^k/( 3^k - 1 - 6*x*18^k/( x*6^(k+1)+(k+1)/G(k+1)))); (continued fraction, 3-step ). - Sergei N. Gladkovskii, Jan 10 2012 %o A155611 (PARI) a(n)=6^n-3^n+1 \\ _Charles R Greathouse IV_, Jan 09 2012 %Y A155611 Cf. A155596-A155610. %K A155611 nonn,easy %O A155611 0,2 %A A155611 _Mohammad K. Azarian_, Jan 26 2009