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 A341768 #6 Feb 19 2021 09:45:16
%S A341768 0,-2,-2,3,16,40,78,133,208,306,430,583,768,988,1246,1545,1888,2278,
%T A341768 2718,3211,3760,4368,5038,5773,6576,7450,8398,9423,10528,11716,12990,
%U A341768 14353,15808,17358,19006,20755,22608,24568,26638,28821,31120,33538,36078,38743,41536,44460
%N A341768 a(n) = n * (binomial(n,2) - 2).
%C A341768 The n-th second n-gonal number.
%H A341768 <a href="/index/Pol#polygonal_numbers">Index to sequences related to polygonal numbers</a>
%H A341768 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-6,4,-1).
%F A341768 G.f.: -x*(2 - 6*x + x^2)/(1 - x)^4.
%F A341768 E.g.f.: -exp(x)*x*(4 - 2*x - x^2)/2.
%F A341768 a(n) = n^2*(n - 1)/2 - 2*n.
%e A341768 a(7) = A147875(7) = A000566(-7) = 133.
%t A341768 Table[n (Binomial[n, 2] - 2), {n, 0, 45}]
%t A341768 LinearRecurrence[{4, -6, 4, -1}, {0, -2, -2, 3}, 46]
%t A341768 CoefficientList[Series[-x (2 - 6 x + x^2)/(1 - x)^4, {x, 0, 45}], x]
%Y A341768 Cf. A005449, A005564, A006002, A014105, A033954, A034856, A045944, A060354, A062728, A135705, A147875, A179986, A292551.
%K A341768 sign,easy
%O A341768 0,2
%A A341768 _Ilya Gutkovskiy_, Feb 19 2021