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 A341441 #23 Feb 12 2021 18:53:19 %S A341441 1,35,287,1302,4257,11297,25935,53516,101745,181279,306383,495650, %T A341441 772785,1167453,1716191,2463384,3462305,4776219,6479551,8659118, %U A341441 11415425,14864025,19136943,24384164,30775185,38500631,47773935,58833082,71942417,87394517,105512127 %N A341441 Total number of triangles visible in a regular (2n+1)-gon with all diagonals drawn. %C A341441 For n=1, an equilateral triangle, there is no diagonal, and thus the polygon itself is the only triangle. %H A341441 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-21,35,-35,21,-7,1). %F A341441 a(n) = n*(2*n+1)*(2*n-1)*(2*n^3+21*n^2-2*n+9)/90. %F A341441 G.f.: x*(x^5+20*x^4+7*x^3-63*x^2-28*x-1)/(x-1)^7. - _Alois P. Heinz_, Feb 11 2021 %F A341441 E.g.f.: exp(x)*x*(90 + 1485*x + 2775*x^2 + 1350*x^3 + 204*x^4 + 8*x^5)/90. - _Stefano Spezia_, Feb 12 2021 %Y A341441 Bisection (odd part) of A005732 and of A006600. %K A341441 nonn,easy %O A341441 1,2 %A A341441 _Edward Porcella_, Feb 11 2021