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 A108620 #26 Mar 15 2024 15:20:10
%S A108620 2,4,4,2,0,-3,-6,-4,2,6,6,2,-5,-10,-6,4,10,8,0,-9,-12,-4,11,20,12,-6,
%T A108620 -16,-10,6,19,17,1,-16,-18,-2,16,21,9,-12,-22,-10,12,25,17,-5,-22,-18,
%U A108620 4,22,20,0,-21,-24,-4,23,32,12,-21,-36,-16,23,44,24,-18,-40,-22,18,43,29,-11,-40,-30,10,40,32,-6,-39,-35,3,40,40,2,-36
%N A108620 2*a(n) = A108618(n) + 3*A108619(n).
%C A108620 Floretion Algebra Multiplication Program, FAMP Code: 1vessum(*)seq[ + .5'i + .5'j + .5'k + .5e]
%H A108620 Creighton Dement, <a href="/A108620/b108620.txt">Table of n, a(n) for n = 0..10000</a>
%H A108620 Rémy Sigrist, <a href="/A108620/a108620.png">Colored scatterplot of a(n) for n = 0..10000</a> (where the color is function of n mod 6)
%t A108620 a[0] = b[0] = 1;
%t A108620 f[n_] := Sign[n]*Mod[n, 2];
%t A108620 a[n_] := a[n] = (1/2)*(a[n-1] - 3*b[n-1]) + 3*f[(1/2)*(a[n-1] + b[n-1])] + f[(1/2)*(a[n-1] - 3*b[n-1])] + 1;
%t A108620 b[n_] := b[n] = (1/2)*(a[n-1] + b[n-1]) + 1;
%t A108620 A108620 = Table[(a[n] + 3*b[n])/2, {n, 0, 100}] (* _Jean-François Alcover_, Feb 25 2015, after _Benoit Jubin_ *)
%Y A108620 Cf. A108618, A108619.
%K A108620 easy,sign,look
%O A108620 0,1
%A A108620 _Creighton Dement_, Jun 22 2005