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 A336121 #9 Jul 17 2020 22:57:33 %S A336121 0,0,0,1,0,1,0,1,0,1,0,1,0,1,0,2,0,2,0,1,0,1,0,2,1,1,0,1,0,2,0,3,0,1, %T A336121 1,1,0,1,0,2,0,2,0,1,0,1,0,3,0,1,0,1,0,3,1,2,0,1,0,1,0,1,0,3,1,2,0,1, %U A336121 0,1,0,2,0,1,1,1,0,2,0,3,0,1,0,1,1,1,0,2,0,3,0,1,0,1,1,3,0,2,0,2,0,2,0,2,1 %N A336121 a(1) = 0, and for n > 1, a(n) = [A122111(n) == 3 (mod 4)] + a(A253553(n)). %C A336121 Positions for the first occurrence of each n, for n >= 0, are: 1, 4, 16, 32, 144, 512, 2048, 6912, 20736, 62208, ... %H A336121 Antti Karttunen, <a href="/A336121/b336121.txt">Table of n, a(n) for n = 1..65537</a> %F A336121 a(1) = 0, and for n > 1, a(n) = [A336124(n) == 3] + a(A253553(n)). %F A336121 a(n) = A000120(A336120(n)). %F A336121 a(n) = A292377(A122111(n)). %F A336121 a(n) = A001222(n) - A336123(n). %o A336121 (PARI) %o A336121 A253553(n) = if(n<=2,1,my(f=factor(n), k=#f~); if(f[k,2]>1,f[k,2]--,f[k,1] = precprime(f[k,1]-1)); factorback(f)); %o A336121 A336121(n) = if(1==n,0,(3==A336124(n))+A336121(A253553(n))); %Y A336121 Cf. A000120, A001222, A122111, A253553, A292377, A292383, A336120, A336123, A336124. %Y A336121 Cf. A336119 (positions of zeros). %K A336121 nonn %O A336121 1,16 %A A336121 _Antti Karttunen_, Jul 17 2020