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 A131042 #12 Aug 26 2024 18:31:06
%S A131042 1,2,4,3,5,6,7,8,10,9,11,12,13,14,16,15,17,18,19,20,22,21,23,24,25,26,
%T A131042 28,27,29,30,31,32,34,33,35,36,37,38,40,39,41,42,43,44,46,45,47,48,49,
%U A131042 50,52,51,53,54,55,56,58,57,59,60,61,62,64,63,65,66,67,68,70,69,71,72
%N A131042 Natural numbers A000027 with 6n+3 and 6n+4 terms swapped.
%H A131042 Colin Barker, <a href="/A131042/b131042.txt">Table of n, a(n) for n = 1..1000</a>
%H A131042 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%H A131042 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,1,-1).
%F A131042 a(n) = (24*floor(n/6)+3*n^2-3*n+8+9*floor(n/3)*(3*floor(n/3)-2*n+1)-(3*n^2-7*n+8+3*floor(n/3)*(9*floor(n/3)-6*n+7))*(-1)^floor(n/3))/4. - _Luce ETIENNE_, Apr 08 2017
%F A131042 From _Colin Barker_, Apr 08 2017: (Start)
%F A131042 G.f.: x*(1 + x + 2*x^2 - x^3 + 2*x^4 + x^5) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)).
%F A131042 a(n) = a(n-1) + a(n-6) - a(n-7) for n>7.
%F A131042 (End)
%t A131042 LinearRecurrence[{1,0,0,0,0,1,-1},{1,2,4,3,5,6,7},80] (* _Harvey P. Dale_, Aug 26 2024 *)
%o A131042 (PARI) Vec(x*(1 + x + 2*x^2 - x^3 + 2*x^4 + x^5) / ((1 - x)^2*(1 + x)*(1 - x + x^2)*(1 + x + x^2)) + O(x^100)) \\ _Colin Barker_, Apr 08 2017
%K A131042 nonn,easy
%O A131042 1,2
%A A131042 _Paul Curtz_, Sep 23 2007