%I A000091
%S A000091 1,2,2,2,0,4,2,2,0,0,0,4,2,4,0,2,0,0,2,0,4,0,0,4,0,4,0,4,0,0,2,2,0,0,0,
%T A000091 0,2,4,4,0,0,8,2,0,0,0,0,4,2,0,0,4,0,0,0,4,4,0,0,0,2,4,0,2,0,0,2,0,0,0,
%U A000091 0,0,2,4,0,4,0,8,2,0,0,0,0,8,0,4,0,0,0,0,4,0,4,0,0,4,2,4,0,0,0,0,2,4,0
%N A000091 Multiplicative with a(2^k) = 2 for k >= 1; a(3) = 2, a(3^k) = 0 for k 
               >= 2; a(p) = 0 if p >3 and p == -1 mod 3; a(p) = 2 if p > 3 and p 
               == 1 mod 3.
%H A000091 Christian G. Bower, <a href="b000091.txt">Table of n, a(n) for n=1..2000</
               a>
%p A000091 A000091 := proc(n) local b,d,nt,c; if n = 1 then RETURN(1); fi; c := 
               1; if n mod 2 = 0 then c := c*2; fi; if n mod 3 = 0 then c := c*2; 
               fi; nt := n; while nt mod 2 = 0 do nt := nt/2; od; while nt mod 3 
               = 0 do nt := nt/3; od; if irem(n,9) = 0 then RETURN(0); fi; b := 
               1; for d from 3 to nt do if irem(nt,d) = 0 and isprime(d) then b 
               := b*(1+legendre(-3,d)); fi; od; RETURN(b*c); end;
%Y A000091 Sequence in context: A071295 A103223 A091399 this_sequence A155123 A125938 
               A158851
%Y A000091 Adjacent sequences: A000088 A000089 A000090 this_sequence A000092 A000093 
               A000094
%K A000091 nonn,easy,mult
%O A000091 1,2
%A A000091 N. J. A. Sloane (njas(AT)research.att.com).
%E A000091 Description corrected Mar 02 2004. (The old description defined A000086 
               not this sequence.)