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 A138002 #12 Jun 05 2025 09:55:56 %S A138002 0,0,0,2,1,0,4,2,0,6,5,4,8,5,2,10,5,0,12,10,8,14,9,4,16,8,0,18,15,12, %T A138002 20,15,10,22,15,8,24,20,16,26,18,10,28,16,4,30,25,20,32,21,10,34,17,0, %U A138002 36,30,24,38,29,20,40,28,16,42,35,28,44,31,18,46,27,8,48,40,32,50,33,16,52 %N A138002 a(3*n)=2*n, a(3*n+1)=a(n)+n, a(3*n+2)=2*a(n), a(n)=0 for n<3. %H A138002 Reinhard Zumkeller, <a href="/A138002/b138002.txt">Table of n, a(n) for n = 0..10000</a> %F A138002 a(n) = (n mod 3) * a(floor(n/3)) + (2 - n mod 3) * floor(n/3), a(n) = 0. %F A138002 a(A062318(n)) = 0. %t A138002 a[0]=0;a[n_]:=Mod[n,3]*a[Floor[n/3]]+(2-Mod[n,3])*Floor[n/3];Array[a,79,0] (* _James C. McMahon_, Jun 05 2025 *) %Y A138002 Cf. A025480. %K A138002 nonn %O A138002 0,4 %A A138002 _Reinhard Zumkeller_, Feb 26 2008