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 A172525 #20 Jun 26 2025 14:32:21
%S A172525 111111111,222222222,333333333,444444444,555555555,666666666,
%T A172525 777777777,888888888,999999999,1111111110,1222222221,1333333332,
%U A172525 1444444443,1555555554,1666666665,1777777776,1888888887,1999999998,2111111109,2222222220,2333333331,2444444442,2555555553
%N A172525 a(n) = 111111111 * n.
%H A172525 Vincenzo Librandi, <a href="/A172525/b172525.txt">Table of n, a(n) for n = 1..1000</a>
%H A172525 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A172525 From _Colin Barker_, Aug 20 2014: (Start)
%F A172525 a(n) = 2*a(n-1) - a(n-2).
%F A172525 G.f.: 111111111*x/(x-1)^2. (End)
%F A172525 From _Elmo R. Oliveira_, Jun 25 2025: (Start)
%F A172525 E.g.f.: 111111111*x*exp(x).
%F A172525 a(n) = 12345679*A008591(n). (End)
%t A172525 Table[9 n 12345679, {n, 1, 20}] (* _Vincenzo Librandi_, Aug 20 2014 *)
%t A172525 LinearRecurrence[{2,-1},{111111111,222222222},20] (* _Harvey P. Dale_, Sep 10 2023 *)
%o A172525 (Magma) [9*n*12345679: n in [1..20]]; // _Vincenzo Librandi_, Aug 20 2014
%o A172525 (PARI) Vec(111111111*x/(x-1)^2 + O(x^100)) \\ _Colin Barker_, Aug 20 2014
%Y A172525 Cf. A008591, A021085.
%K A172525 nonn,easy
%O A172525 1,1
%A A172525 _Vincenzo Librandi_, Feb 06 2010