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%I #15 Aug 05 2021 01:31:06
%S 0,0,0,0,0,1,0,0,0,1,0,1,0,1,1,0,0,1,0,1,1,1,0,1,0,1,0,1,0,1,0,0,1,1,
%T 1,1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,1,1,0,1,1,1,1,1,0,1,0,1,1,0,1,1,0,1,
%U 1,1,0,1,0,1,1,1,1,1,0,1,0,1,0,1,1,1,1
%N Characteristic function of numbers with at least two distinct prime factors (A024619).
%C a(n) = 1 iff n is divisible by at least two distinct primes; otherwise 0.
%H Reikku Kulon, <a href="/A143731/b143731.txt">Table of n, a(n) for n = 1..10000</a>
%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%F a(n) = abs(A079872(n)) = A057427(A079275(n)).
%F For n>1: a(n) = 1 - floor(1/A001221(n)). - _Enrique Pérez Herrero_, Aug 13 2012
%t Table[Boole[PrimeNu[n]>1],{n,1,200}] (* _Enrique Pérez Herrero_, Aug 13 2012 *)
%Y Cf. A024619, A079275, A079872, A000961, A001222, A091304, A073093, A001221.
%Y Cf. A215480.
%K easy,nonn
%O 1,1
%A _Reikku Kulon_, Aug 30 2008