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 A250352 #18 Sep 03 2023 18:21:18 %S A250352 8,26,62,122,212,338,506,722,992,1322,1718,2186,2732,3362,4082,4898, %T A250352 5816,6842,7982,9242,10628,12146,13802,15602,17552,19658,21926,24362, %U A250352 26972,29762,32738,35906,39272,42842,46622,50618,54836,59282,63962,68882,74048 %N A250352 Number of length 3 arrays x(i), i=1..3 with x(i) in i..i+n and no value appearing more than 2 times. %C A250352 a(n) = (n+1)^3 - (n-1), where (n+1)^3 is the number of ways of selecting a triple from n+1 numbers in these subintervals, and there are n-1 of these triples, (3,3,3) up to (n-2,n-2,n-2), where all values are the same, which are discarded. - _R. J. Mathar_, Oct 09 2020 %H A250352 R. H. Hardin, <a href="/A250352/b250352.txt">Table of n, a(n) for n = 1..210</a> %H A250352 N. J. A. Sloane, Coordination Sequences, Planing Numbers, and Other Recent Sequences (II), Experimental Mathematics Seminar, Rutgers University, Jan 31 2019, <a href="https://vimeo.com/314786942">Part I</a>, <a href="https://vimeo.com/314790822">Part 2</a>, <a href="https://oeis.org/A320487/a320487.pdf">Slides</a>. (Mentions this sequence) %F A250352 a(n) = n^3 + 3*n^2 + 2*n + 2 = 2*A158842(n+1). %F A250352 From _Colin Barker_, Nov 12 2018: (Start) %F A250352 G.f.: 2*x*(4 - 3*x + 3*x^2 - x^3) / (1 - x)^4. %F A250352 a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4. %F A250352 (End) %e A250352 Some solutions for n=6: %e A250352 2 0 1 2 6 4 0 1 0 0 2 4 6 2 4 0 %e A250352 4 4 7 7 2 4 2 3 1 6 1 2 3 6 5 5 %e A250352 6 4 7 2 4 7 8 5 3 6 4 7 5 8 8 2 %Y A250352 Row 3 of A250351. %K A250352 nonn,easy %O A250352 1,1 %A A250352 _R. H. Hardin_, Nov 19 2014