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 A274586 #24 Nov 13 2023 11:28:11 %S A274586 3,21,132,429,1272,2826,5640,10461,17094,26847,41046,61041,84051, %T A274586 118974,157209,204393,264855,346524,428880,541683,654087,793611, %U A274586 961179,1167468,1357515,1615209,1891980,2198019,2530275,2957808,3341439,3860652,4371006,4959636,5572167,6277722,6950064,7859406,8763780,9722571,10687506,11934912,13029834,14450598,15805026,17250795,18863397,20763204,22372839,24450474 %N A274586 Number of edges formed by sides and straight "chords" in a right triangle when each side is divided by vertices into n equal segments. %F A274586 By the Euler characteristic, a(n) = A274585(n) + A092867(n) - 1 = A092866(n) + A092867(n) + 3n - 1. %Y A274586 Cf. A092866, A092867, A274585. %Y A274586 If the boundary points are in general position, we get A367117, A213827, A367118, A367119. - _N. J. A. Sloane_, Nov 09 2023 %K A274586 nonn %O A274586 1,1 %A A274586 _Cynthia Miaina Rasamimanananivo_ and _Max Alekseyev_, Jun 29 2016, Sep 02 2016