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 A322180 #15 Dec 01 2018 08:21:56
%S A322180 1,1,5,36,466,8942,240366,8576860,392952468,22470271108
%N A322180 The number of permutations of {1,2,...,n,1,2,...,n} with the property that there are k or fewer numbers between the two k's in the set for k=1,...,n.
%e A322180 In case of n = 2.
%e A322180 | permutation
%e A322180 --+-------------
%e A322180 1 | [1, 1, 2, 2]
%e A322180 2 | [1, 2, 1, 2]
%e A322180 3 | [2, 1, 1, 2]
%e A322180 4 | [2, 1, 2, 1]
%e A322180 5 | [2, 2, 1, 1]
%Y A322180 Cf. A176127, A322179.
%K A322180 nonn,more
%O A322180 0,3
%A A322180 _Seiichi Manyama_, Nov 30 2018
%E A322180 a(9) from _Alois P. Heinz_, Nov 30 2018