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 A017221 #74 Apr 10 2025 17:12:58
%S A017221 5,14,23,32,41,50,59,68,77,86,95,104,113,122,131,140,149,158,167,176,
%T A017221 185,194,203,212,221,230,239,248,257,266,275,284,293,302,311,320,329,
%U A017221 338,347,356,365,374,383,392,401,410,419,428,437,446,455,464,473,482
%N A017221 a(n) = 9*n + 5.
%C A017221 Numbers whose digital root is 5. - _Halfdan Skjerning_, Mar 15 2018
%D A017221 R. K. Guy, Unsolved Problems in Number Theory, Springer, 1st edition, 1981. See section D5.
%H A017221 Vincenzo Librandi, <a href="/A017221/b017221.txt">Table of n, a(n) for n = 0..5000</a>
%H A017221 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>.
%H A017221 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A017221 G.f.: (5+4*x)/(1-x)^2. - _R. J. Mathar_, Mar 20 2018
%F A017221 From _G. C. Greubel_, Jan 06 2023: (Start)
%F A017221 a(n) = a(n-1) + 9, with a(0) = 5.
%F A017221 E.g.f.: (5 + 9*x)*exp(x). (End)
%F A017221 From _Elmo R. Oliveira_, Apr 10 2025: (Start)
%F A017221 a(n) = 2*a(n-1) - a(n-2).
%F A017221 a(n) = A016789(3*n+1). (End)
%p A017221 seq(9*w+5, w=0..100); # _Matt C. Anderson_, May 18 2017
%t A017221 Range[5, 1000, 9] (* _Vladimir Joseph Stephan Orlovsky_, May 28 2011 *)
%t A017221 9*Range[0,60]+5 (* or *) LinearRecurrence[{2,-1},{5,14},60] (* _Harvey P. Dale_, Jul 05 2021 *)
%o A017221 (PARI) forstep(n=5,500,9,print1(n", ")) \\ _Charles R Greathouse IV_, May 28 2011
%o A017221 (Magma) [9*n+5: n in [0..60]]; // _Vincenzo Librandi_, Jul 24 2011
%o A017221 (SageMath) [9*n+5 for n in range(51)] # _G. C. Greubel_, Jan 06 2023
%Y A017221 Sequences of the form (9*n+5)^k: this sequence (k=1), A017222 (k=2), A017223 (k=3), A017224 (k=4), A017225 (k=5), A017226 (k=6), A017227 (k=7), A017228 (k=8), A017229 (k=9), A017230 (k=10), A017231 (k=11).
%Y A017221 Cf. A008591, A016789, A017209.
%Y A017221 Cf. similar sequences with closed form (2*k-1)*n+k listed in A269044.
%K A017221 nonn,easy
%O A017221 0,1
%A A017221 _N. J. A. Sloane_