%I A066247
%S A066247 0,0,0,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,
%T A066247 1,0,1,1,1,0,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,1,0,1,1,1,
%U A066247 0,1,0,1,1,1,1,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1,1,1,1,0,1,1,1,0,1,0,1,1
%N A066247 Characteristic function of composite numbers: 1 if n is composite else 
               0.
%C A066247 a(n) = signum(A066246(n)), where signum = A057427. For n > 1: a(n) = 
               1 - A010051(n) = A005171(n).
%H A066247 <a href="Sindx_Ch.html#char_fns">Index entries for characteristic functions</
               a>
%F A066247 a(n)={[(n+1)-(n-1)!^2] mod n}, with n>=1 - Paolo P. Lava (ppl(AT)spl.at), 
               Jan 29 2008
%p A066247 P:=proc(n) local i; for i from 1 by 1 to n do print(((i+1)-(i-1)!^2) 
               mod i); od; end: P(100); - Paolo P. Lava (ppl(AT)spl.at), Jan 29 
               2008
%Y A066247 Cf. A002808, A010051, A005171.
%Y A066247 Sequence in context: A064911 A099618 A106002 this_sequence A151774 A095792 
               A093385
%Y A066247 Adjacent sequences: A066244 A066245 A066246 this_sequence A066248 A066249 
               A066250
%K A066247 nonn
%O A066247 1,1
%A A066247 Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Dec 09 2001