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 A269620 #8 Jan 25 2019 08:28:12 %S A269620 15,78,249,612,1275,2370,4053,6504,9927,14550,20625,28428,38259,50442, %T A269620 65325,83280,104703,130014,159657,194100,233835,279378,331269,390072, %U A269620 456375,530790,613953,706524,809187,922650,1047645,1184928,1335279 %N A269620 Number of length-4 0..n arrays with no repeated value differing from the previous repeated value by other than plus two, zero or minus 1. %H A269620 R. H. Hardin, <a href="/A269620/b269620.txt">Table of n, a(n) for n = 1..210</a> %F A269620 Empirical: a(n) = n^4 + 4*n^3 + 5*n^2 + 5*n. %F A269620 Conjectures from _Colin Barker_, Jan 25 2019: (Start) %F A269620 G.f.: 3*x*(5 + x + 3*x^2 - x^3) / (1 - x)^5. %F A269620 a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5. %F A269620 (End) %e A269620 Some solutions for n=8: %e A269620 ..2. .5. .6. .8. .5. .2. .1. .4. .1. .5. .5. .6. .0. .5. .7. .2 %e A269620 ..2. .7. .2. .7. .2. .2. .0. .6. .0. .1. .6. .0. .3. .6. .1. .5 %e A269620 ..6. .5. .7. .0. .2. .3. .6. .7. .0. .5. .1. .2. .5. .2. .7. .2 %e A269620 ..3. .2. .6. .0. .5. .8. .0. .6. .7. .6. .2. .2. .4. .4. .2. .4 %Y A269620 Row 4 of A269619. %K A269620 nonn %O A269620 1,1 %A A269620 _R. H. Hardin_, Mar 01 2016