%I A086823
%S A086823 0,0,1,1,1,1,1,0,0,1,1,1,1,1,0,0,1,0,1,1,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,
%T A086823 0,1,1,0,0,1,0,1,1,0,1,1,0,0,0,0,1,1,0,0,0,0,1,1,1,1,1,0,0,0,0,1,1,0,0,
%U A086823 1,0,1,1,0,1,0,0,1,0,0,1,1,1,0,1,0,0,1,0,0,1,0,1,0,0,1,0,0,0,1,0,1,0,1
%V A086823 0,0,1,1,1,1,1,0,0,1,1,-1,1,1,0,0,1,0,1,-1,0,1,1,0,0,1,0,-1,1,0,1,0,0,
               1,0,0,1,1,0,0,1,
%W A086823 0,1,-1,0,1,1,0,0,0,0,-1,1,0,0,0,0,1,1,1,1,1,0,0,0,0,1,-1,0,0,1,0,1,1,
               0,-1,0,0,1,0,0,1,
%X A086823 1,1,0,1,0,0,1,0,0,-1,0,1,0,0,1,0,0,0,1,0,1,0,1
%N A086823 Coefficient of x^2 in the n-th cyclotomic polynomial. (The same as the 
               coefficient of x^(phi(n)-2) ).
%F A086823 if n is odd a(n) = 1/2 * mu(n)*(mu(n)-1) if n is even a(n) = 1/2 * mu(n)*(mu(n)-1) 
               - mu(n/2).
%o A086823 (PARI) a(n) = polcoeff(polcyclo(n), 2); (Wasserman)
%Y A086823 Cf. A008683, A000010.
%Y A086823 Sequence in context: A131735 A131736 A152228 this_sequence A104121 A157928 
               A159075
%Y A086823 Adjacent sequences: A086820 A086821 A086822 this_sequence A086824 A086825 
               A086826
%K A086823 sign
%O A086823 3,1
%A A086823 Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 07 2003
%E A086823 More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Mar 29 
               2005