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 A099991 #24 Aug 12 2021 05:04:00 %S A099991 -1,0,1,0,1,0,1,0,0,0,1,0,1,0,-1,0,1,0,1,0,-1,0,1,0,0,0,0,0,1,0,1,0, %T A099991 -1,0,-1,0,1,0,-1,0,1,0,1,0,0,0,1,0,0,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,0, %U A099991 0,-1,0,1,0,-1,0,1,0,1,0,0,0,-1,0,1,0,0,0,1,0,-1,0,-1,0,1,0,-1,0,-1,0,-1,0,1,0,0,0,1,0,1,0,1 %N A099991 a(n) = Moebius(2n). %C A099991 b(n) = -a(n) is multiplicative with b(2^e) = 0, b(p) = -1 if p >= 3, 0 otherwise. - _David W. Wilson_, Jun 12 2005 %H A099991 Antti Karttunen, <a href="/A099991/b099991.txt">Table of n, a(n) for n = 1..10000</a> %F A099991 a(n) = A008683(2n). - _Wesley Ivan Hurt_, Dec 17 2013 %p A099991 with(numtheory); A099991:=n->mobius(2*n); seq(A099991(n), n=1..100); # _Wesley Ivan Hurt_, Dec 17 2013 %t A099991 MoebiusMu[2*Range[110]] (* _Harvey P. Dale_, Jul 13 2012 *) %o A099991 (PARI) A099991(n) = moebius(2*n); \\ _Antti Karttunen_, Sep 14 2017 %Y A099991 Bisection of A008683. Cf. A099990. %K A099991 sign,easy %O A099991 1,1 %A A099991 _N. J. A. Sloane_, Nov 20 2004