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 A161365 #21 Nov 04 2024 16:12:50
%S A161365 9,9,19,19,29,29,39,39,49,49,59,59,69,69,79,79,89,89,99,99,109,109,
%T A161365 119,119,129,129,139,139,149,149,159,159,169,169,179,179,189,189,199,
%U A161365 199,209,209,219,219,229,229,239,239,249,249,259,259,269,269,279,279,289
%N A161365 a(n) = 3/2 + 5*n - 5*(-1)^n/2.
%H A161365 Vincenzo Librandi, <a href="/A161365/b161365.txt">Table of n, a(n) for n = 1..1000</a>
%H A161365 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A161365 a(n) = 10*n - a(n-1) - 2, n > 1.
%F A161365 a(n+1) = A017377(floor(n/2)). - _R. J. Mathar_, Jan 05 2011
%F A161365 G.f.: x*(9+x^2) / ( (1+x)*(x-1)^2 ). - _R. J. Mathar_, Jan 05 2011
%t A161365 LinearRecurrence[{1, 1, -1}, {9, 9, 19}, 60] (* _Vincenzo Librandi_, Mar 02 2012 *)
%t A161365 Table[3/2+5n-(5(-1)^n)/2,{n,60}] (* or *) nxt[{n_,a_}]:={n+1,10(n+1)-a-2}; NestList[nxt,{1,9},60][[;;,2]] (* _Harvey P. Dale_, Nov 04 2024 *)
%o A161365 (Magma) I:=[9, 9, 19]; [n le 3 select I[n] else Self(n-1)+Self(n-2)-Self(n-3): n in [1..60]]; // _Vincenzo Librandi_, Mar 02 2012
%o A161365 (PARI) for(n=1, 60, print1(3/2+5*n-5*(-1)^n/2", ")); \\ _Vincenzo Librandi_, Mar 02 2012
%K A161365 nonn,easy
%O A161365 1,1
%A A161365 _Vincenzo Librandi_, Nov 25 2009
%E A161365 Definition rewritten by _R. J. Mathar_, Jan 05 2011