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 A318161 #8 Sep 20 2019 03:51:11
%S A318161 1,1,18,195,1652,12825,96030,705341,5116200,36773397,262462010,
%T A318161 1862790699,13160496684,92624149475,649794035142,4545979700445,
%U A318161 31727803153232,220975193536845,1536191185018770,10661898343645847,73890140441316420,511405029708269529
%N A318161 Number of compositions of 2n into exactly 2n nonnegative parts with largest part n.
%H A318161 Alois P. Heinz, <a href="/A318161/b318161.txt">Table of n, a(n) for n = 0..1204</a>
%F A318161 a(n) = A180281(2n,n).
%F A318161 For n>0, a(n) = n - 2*n^2 + 2*n*binomial(3*n - 2, n). - _Vaclav Kotesovec_, Sep 20 2019
%e A318161 a(2) = 18: 0022, 0112, 0121, 0202, 0211, 0220, 1012, 1021, 1102, 1120, 1201, 1210, 2002, 2011, 2020, 2101, 2110, 2200.
%t A318161 Flatten[{1, Table[n - 2*n^2 + 2*n*Binomial[3*n - 2, n], {n, 1, 20}]}] (* _Vaclav Kotesovec_, Sep 20 2019 *)
%Y A318161 Bisection of A318160 (even part).
%Y A318161 Cf. A180281.
%K A318161 nonn
%O A318161 0,3
%A A318161 _Alois P. Heinz_, Aug 19 2018