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 A326658 #21 Sep 26 2019 03:42:02
%S A326658 1,0,7,8,17,20,31,36,49,56,71,80,97,108,127,140,161,176,199,216,241,
%T A326658 260,287,308,337,360,391,416,449,476,511,540,577,608,647,680,721,756,
%U A326658 799,836,881,920,967,1008,1057,1100,1151,1196,1249,1296,1351,1400,1457,1508,1567,1620,1681
%N A326658 a(n) = 6*floor(n/2) + ceiling((n-1)^2/2).
%C A326658 a(n) gives the maximum number of inversions in a permutation on n + 3 symbols consisting of a single n-cycle and 3 fixed points.
%C A326658 Sequence is a diagonal of A326296.
%H A326658 Colin Barker, <a href="/A326658/b326658.txt">Table of n, a(n) for n = 0..1000</a>
%H A326658 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A326658 a(n) = 6*floor(n/2) + ceiling((n-1)^2/2).
%F A326658 a(n) = A326296(3 + n, n) for n > 0.
%F A326658 From _Colin Barker_, Sep 13 2019: (Start)
%F A326658 G.f.: (1 - 2*x + 7*x^2 - 4*x^3) / ((1 - x)^3*(1 + x)).
%F A326658 a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4) for n >= 4.
%F A326658 a(n) = (-3 + 7*(-1)^n + 8*n + 2*n^2) / 4.
%F A326658 (End)
%t A326658 Table[6*Floor[n/2] + Ceiling[(n - 1)^2/2], {n, 80}] (* _Wesley Ivan Hurt_, Sep 13 2019 *)
%o A326658 (PARI) a(n) = 6*floor(n/2) + ceil((n-1)^2/2) \\ _Andrew Howroyd_, Sep 23 2019
%o A326658 (PARI) Vec((1 - 2*x + 7*x^2 - 4*x^3) / ((1 - x)^3*(1 + x)) + O(x^40)) \\ _Andrew Howroyd_, Sep 23 2019
%Y A326658 Diagonal of A326296.
%K A326658 nonn,easy
%O A326658 0,3
%A A326658 _M. Ryan Julian Jr._, Sep 12 2019