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 A177321 #13 May 16 2020 01:34:50 %S A177321 1,2,416,664958,1792874048,6232521421502,25328979140590460, %T A177321 114573118435555703030,560523113474283819256640, %U A177321 2911820015993491302722966990,15861703283168731825003935183416,89796737967084981726163781067177194,524830705066715697873367329722967841532 %N A177321 Number of permutations of n copies of 1..9 with all adjacent differences <= 1 in absolute value. %H A177321 Andrew Howroyd, <a href="/A177321/b177321.txt">Table of n, a(n) for n = 0..100</a> %Y A177321 Row n=9 of A331562. %K A177321 nonn %O A177321 0,2 %A A177321 _R. H. Hardin_, May 06 2010 %E A177321 a(0)=1 prepended by _Alois P. Heinz_, Jan 20 2020 %E A177321 Terms a(6) and beyond from _Andrew Howroyd_, May 15 2020