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 A028283 #20 Jun 05 2021 06:03:22 %S A028283 1,4,10,32,110,392,1428,5280,19734,74360,281996,1074944,4115020, %T A028283 15808912,60917800,235350720,911315430,3535767000,13742347740, %U A028283 53495534400,208537056420,813950932080,3180614712600,12441628655040 %N A028283 Central elements in 4-Pascal triangle A028275 (by row). %C A028283 Equals A000984, [1, 2, 6, 20, 70, ...] convolved with [1, 2, 0, 0, 0, ...]. - _Gary W. Adamson_, Jun 05 2009 %F A028283 a(n) = 2*A051960(n-1). %F A028283 a(n) = 2*A000108(n)*(3n-1). - _Ralf Stephan_, Aug 24 2003 %Y A028283 Cf. A000108, A028275, A051960. %K A028283 nonn,easy %O A028283 0,2 %A A028283 _Mohammad K. Azarian_