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 A259754 #30 Aug 30 2016 20:11:12
%S A259754 3,9,15,18,21,27,33,39,42,45,51,57,63,66,69,75,81,87,90,93,99,105,111,
%T A259754 114,117,123,129,135,138,141,147,153,159,162,165,171,177,183,186,189,
%U A259754 195,201,207,210,213,219,225,231,234,237,243,249,255,258,261,267
%N A259754 Numbers that are congruent to {3,9,15,18,21} mod 24.
%C A259754 Original name: Numbers n such that n/A259748(n) = 3/2.
%H A259754 Danny Rorabaugh, <a href="/A259754/b259754.txt">Table of n, a(n) for n = 1..10000</a>
%H A259754 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,1,-1).
%F A259754 A259748(a(n))/a(n) = 2/3.
%F A259754 a(n) = 3*A047584(n). - _Michel Marcus_, Jul 18 2015
%F A259754 From _Colin Barker_, Aug 25 2016: (Start)
%F A259754 a(n) = a(n-1)+a(n-5)-a(n-6) for n>6.
%F A259754 G.f.: 3*x*(1+x)*(1+x+x^2+x^4) / ((1-x)^2*(1+x+x^2+x^3+x^4)).
%F A259754 (End)
%t A259754 A[n_] := A[n] = Sum[a b, {a, 1, n}, {b, a + 1, n}]; Select[Range[200], Mod[A[#], #]/# == 2/3 &]
%t A259754 Rest@ CoefficientList[Series[3 x (1 + x) (1 + x + x^2 + x^4)/((1 - x)^2*(1 + x + x^2 + x^3 + x^4)), {x, 0, 56}], x] (* _Michael De Vlieger_, Aug 25 2016 *)
%t A259754 LinearRecurrence[{1,0,0,0,1,-1},{3,9,15,18,21,27},60] (* _Harvey P. Dale_, Aug 30 2016 *)
%o A259754 (PARI) Vec(3*x*(1+x)*(1+x+x^2+x^4)/((1-x)^2*(1+x+x^2+x^3+x^4)) + O(x^100)) \\ _Colin Barker_, Aug 25 2016
%Y A259754 Cf. A000914.
%Y A259754 Other sequences of numbers n such that A259748(n)/n equals a constant: A008606, A073762, A259749, A259750, A259751, A259752, A259755.
%K A259754 nonn,easy
%O A259754 1,1
%A A259754 _José María Grau Ribas_, Jul 12 2015
%E A259754 Better name from _Danny Rorabaugh_, Oct 22 2015