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 A307559 #20 Jul 22 2022 08:01:49 %S A307559 0,0,2,6,12,24,40,60,90,126,168,224,288,360,450,550,660,792,936,1092, %T A307559 1274,1470,1680,1920,2176,2448,2754,3078,3420,3800,4200,4620,5082, %U A307559 5566,6072,6624,7200,7800,8450,9126,9828,10584,11368,12180,13050,13950,14880,15872 %N A307559 a(n) = floor(n/3)*(n - floor(n/3))*(n - floor(n/3) - 1). %C A307559 a(n) is an upper bound for the irregularity of a graph with n vertices (see Theorem 3.2 of the Tavakoli et al. reference). %H A307559 M. Tavakoli, F. Rahbarnia, M. Mirzavaziri, A. R. Ashrafi, and I. Gutman, <a href="https://imi.pmf.kg.ac.rs/kjm/pub/13681216896539_tavakoligutman.pdf">Extremely irregular graphs</a>, Kragujevac J. Math., 37 (1), 2013, 135-139. %H A307559 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,2,-4,2,-1,2,-1). %F A307559 a(n) = 2*A200067(n). %F A307559 G.f.: 2*x^3*(1+x)*(1+x^2) / ( (1+x+x^2)^2*(x-1)^4 ). - _R. J. Mathar_, Jul 22 2022 %e A307559 a(4) = floor(4/3)*(4 - floor(4/3))*(4-floor(4/3)-1) = 1*3*2 = 6. %p A307559 a:=n->floor(n/3)*(n-floor(n/3))*(n-floor(n/3)-1): seq(a(n), n=1..50); %Y A307559 Cf. A200067. %K A307559 nonn,easy %O A307559 1,3 %A A307559 _Emeric Deutsch_, Apr 14 2019