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 A017197 #56 Jan 22 2023 10:39:16
%S A017197 3,12,21,30,39,48,57,66,75,84,93,102,111,120,129,138,147,156,165,174,
%T A017197 183,192,201,210,219,228,237,246,255,264,273,282,291,300,309,318,327,
%U A017197 336,345,354,363,372,381,390,399,408,417,426,435,444,453,462,471,480
%N A017197 a(n) = 9*n + 3.
%C A017197 Numbers whose digital root is 3. - _Cino Hilliard_, Dec 26 2006
%C A017197 a(n)^2 = A017198(n). - _Reinhard Zumkeller_, Jul 13 2010
%H A017197 G. C. Greubel, <a href="/A017197/b017197.txt">Table of n, a(n) for n = 0..1000</a>
%H A017197 Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>
%H A017197 Luis Manuel Rivera, <a href="http://arxiv.org/abs/1406.3081">Integer sequences and k-commuting permutations</a>, arXiv preprint arXiv:1406.3081 [math.CO], 2014-2015.
%H A017197 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A017197 a(n) = a(n-1) + 9.
%F A017197 a(n) = 3*A016777(n).
%F A017197 a(n) = A092292(n) + A092293(n) + A092296(n).
%F A017197 From _Philippe Deléham_, Mar 10 2004: (Start)
%F A017197 Sum_{n>=0} (-1)^n / a(n) = (Pi / sqrt(3) + log(2))/9.
%F A017197 G.f.: 3*(1+2*x)/(1-x)^2. (End)
%F A017197 a(n) = 3*(6*n-1) - a(n-1) with a(0)=3. - _Vincenzo Librandi_, Nov 20 2010
%F A017197 E.g.f.: 3*(1 + 3*x)*exp(x). - _G. C. Greubel_, Dec 03 2019
%p A017197 seq(9*n+3, n=0..60); # _G. C. Greubel_, Dec 03 2019
%t A017197 3*(3*Range[60] -2) (* _G. C. Greubel_, Dec 03 2019 *)
%t A017197 LinearRecurrence[{2,-1},{3,12},80] (* or *) NestList[#+9&,3,80] (* _Harvey P. Dale_, Jan 22 2023 *)
%o A017197 (PARI) vector(60, n, 3*(3*n-2) ) \\ _G. C. Greubel_, Dec 03 2019
%o A017197 (Sage) [i+3 for i in range(480) if gcd(i,9) == 9] # _Zerinvary Lajos_, May 20 2009
%o A017197 (Haskell)
%o A017197 a017197 = (+ 3) . (* 9)
%o A017197 a017197_list = [3, 12 ..] -- _Reinhard Zumkeller_, Jun 04 2015
%o A017197 (Magma) [9*n+3: n in [0..60]]; // _G. C. Greubel_, Dec 03 2019
%o A017197 (GAP) List([0..60], n-> 9*n+3); # _G. C. Greubel_, Dec 03 2019
%Y A017197 Cf. A092292, A092293, A092296.
%Y A017197 Cf. sequences with general form q*(q*n+1): A016825 (q=2), this sequence (q=3), A119413 (q=4), ... - _Vladimir Joseph Stephan Orlovsky_, Feb 16 2009
%Y A017197 Cf. A016777.
%K A017197 nonn,easy
%O A017197 0,1
%A A017197 _N. J. A. Sloane_
%E A017197 More terms from _Cino Hilliard_, Dec 26 2006