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 A198766 #21 Mar 09 2025 12:42:13
%S A198766 3,17,87,437,2187,10937,54687,273437,1367187,6835937,34179687,
%T A198766 170898437,854492187,4272460937,21362304687,106811523437,534057617187,
%U A198766 2670288085937,13351440429687,66757202148437,333786010742187,1668930053710937
%N A198766 a(n) = (7*5^n - 1)/2.
%H A198766 Vincenzo Librandi, <a href="/A198766/b198766.txt">Table of n, a(n) for n = 0..1000</a>
%H A198766 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (6,-5).
%F A198766 a(n) = 5*a(n-1)+2.
%F A198766 a(n) = 6*a(n-1)-5*a(n-2), n>1.
%F A198766 G.f.: (3 - x)/(1 - 6*x + 5*x^2). - _Vincenzo Librandi_, Jan 04 2013
%F A198766 E.g.f.: exp(x)*(7*exp(4*x) - 1)/2. - _Stefano Spezia_, Mar 08 2025
%t A198766 CoefficientList[Series[(3 - x)/(1 - 6*x + 5*x^2), {x, 0, 30}], x] (* _Vincenzo Librandi_, Jan 04 2013 *)
%t A198766 LinearRecurrence[{6,-5},{3,17},30] (* _Harvey P. Dale_, Jan 23 2015 *)
%o A198766 (Magma) [(7*5^n-1)/2: n in [0..30]];
%Y A198766 Cf. A024049, A057651, A081655.
%K A198766 nonn,easy
%O A198766 0,1
%A A198766 _Vincenzo Librandi_, Oct 30 2011