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%I #10 Jan 08 2019 19:07:09
%S 0,0,0,0,0,0,0,0,1,1,0,0,0,0,1,1,0,0,0,0,1,1,0,0,1,1,1,1,0,0,0,0,1,1,
%T 1,1,0,0,1,1,0,0,0,0,1,1,0,0,1,1,1,1,0,0,1,1,1,1,0,0,0,0,1,1,1,1,0,0,
%U 1,1,0,0,0,0,1,1,1,1,0,0,1,1,0,0,1,1,1,1,0,0,1,1,1,1,1,1,0,0,1,1,0,0,0,0,1
%N a(n) = 1 if both n and n-1 are composite, 0 otherwise.
%C Characteristic function of A005381.
%H Antti Karttunen, <a href="/A323162/b323162.txt">Table of n, a(n) for n = 1..65537</a>
%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%F a(1) = 0; for n > 1, a(n) = (1-A010051(n-1)) * (1-A010051(n)).
%F a(A005381(n)) = 1, a(A093515(n)) = 0.
%F For n >= 4, a(n) = 1-A090405(n-2).
%t Map[Boole[AllTrue[#, CompositeQ]] &, Partition[Range[0, 120], 2, 1]] (* _Michael De Vlieger_, Jan 07 2019 *)
%o (PARI) A323162(n) = ((n>1)&&(!isprime(n))&&(!isprime(n-1)));
%Y Cf. A005381, A010051, A090405, A093515, A323161.
%K nonn
%O 1
%A _Antti Karttunen_, Jan 07 2019
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