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 A173193 #32 Jun 18 2025 00:58:53
%S A173193 7,27,227,2227,22227,222227,2222227,22222227,222222227,2222222227,
%T A173193 22222222227,222222222227,2222222222227,22222222222227,
%U A173193 222222222222227,2222222222222227,22222222222222227,222222222222222227,2222222222222222227,22222222222222222227,222222222222222222227
%N A173193 a(n) = (2*10^n + 43)/9.
%C A173193 n-1 2's followed by a 7.
%H A173193 Markus Tervooren, <a href="https://factordb.com/index.php?query=%282%2A10%5Ex%2B43%29%2F9">Factorizations of (2)w7</a>.
%H A173193 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A173193 a(n) = 10*a(n-1) - 43 with n>1, a(1)=7. - _Vincenzo Librandi_, Dec 05 2010
%F A173193 a(n) = a(n-1) + 2*10^(n-1) with n>1, a(1)=7. - _Zak Seidov_, Dec 05 2010
%F A173193 From _Colin Barker_, Jan 24 2013: (Start)
%F A173193 a(n) = 11*a(n-1) - 10*a(n-2).
%F A173193 G.f.: -x*(50*x-7)/((x-1)*(10*x-1)). (End)
%F A173193 E.g.f.: -5 + exp(x)*(43 + 2*exp(9*x))/9. - _Elmo R. Oliveira_, Jun 17 2025
%t A173193 Table[FromDigits[PadLeft[{7},n,2]],{n,20}] (* or *) LinearRecurrence[{11,-10},{7,27},20] (* _Harvey P. Dale_, Jan 06 2023 *)
%o A173193 (PARI) my(x='x+O('x^22)); Vec(x*(7-50*x)/((1-11*x+10*x^2))) \\ _Elmo R. Oliveira_, Jun 17 2025
%K A173193 easy,nonn
%O A173193 1,1
%A A173193 _Ivan Panchenko_, Feb 12 2010
%E A173193 More terms from _Vincenzo Librandi_, Feb 24 2010
%E A173193 a(19)-a(21) from _Elmo R. Oliveira_, Jun 17 2025