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 A152494 #12 May 19 2020 15:10:51
%S A152494 0,1,19,235,2539,26119,263863,2648107,26513875,265250287,2652876847,
%T A152494 26530008499,265304159371,2653054879735,26530591844071,
%U A152494 265306057146811,2653061016284227,26530611583384063,265306120353746335,2653061217872021443,26530612224048411643
%N A152494 1/3 of the number of permutations of 2 indistinguishable copies of 1..n with exactly 2 local maxima.
%H A152494 Andrew Howroyd, <a href="/A152494/b152494.txt">Table of n, a(n) for n = 1..200</a>
%H A152494 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (16,-69,90).
%F A152494 a(n) = (13*10^(n-1) - 13*3^(n-1) - 14*(n-1)*3^(n-1))/49. - _Andrew Howroyd_, May 10 2020
%F A152494 From _Colin Barker_, May 19 2020: (Start)
%F A152494 G.f.: x*(1 + 3*x) / ((1 - 3*x)^2*(1 - 10*x)).
%F A152494 a(n) = 16*a(n-1) - 69*a(n-2) + 90*a(n-3) for n>3.
%F A152494 (End)
%o A152494 (PARI) a(n) = {(13*10^(n-1) - 13*3^(n-1) - 14*(n-1)*3^(n-1))/49} \\ _Andrew Howroyd_, May 10 2020
%o A152494 (PARI) concat(0, Vec(x*(1 + 3*x) / ((1 - 3*x)^2*(1 - 10*x)) + O(x^20))) \\ _Colin Barker_, May 19 2020
%Y A152494 Cf. A334773.
%K A152494 nonn,easy
%O A152494 1,3
%A A152494 _R. H. Hardin_, Dec 06 2008
%E A152494 Terms a(12) and beyond from _Andrew Howroyd_, May 10 2020