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a(n) = 4^(composite(n) - 4) mod composite(n+4).
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%I #15 Dec 06 2020 13:53:10

%S 1,4,4,4,0,16,16,16,16,16,21,10,1,16,4,0,31,18,16,4,16,1,24,16,36,34,

%T 18,16,46,4,16,16,28,26,16,7,54,4,16,16,0,16,64,64,58,4,16,70,49,64,9,

%U 22,64,55,64,16,1,44,25,56,64,74,48,70,74,49,64,44,1,4,52,48,79,36,88,56,58,64,112,31

%N a(n) = 4^(composite(n) - 4) mod composite(n+4).

%H Harvey P. Dale, <a href="/A176101/b176101.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = 4^(A002808(n) - 4) mod A002808(n+4).

%e a(2)=6 because 4^(composite(2) - 4) mod composite(2+4) = 16 mod 12 = 4.

%p A176101 := proc(n) modp(4^(A002808(n)-4) ,A002808(n+4)) ; end proc:

%p seq(A176101(n),n=1..80) ; # _R. J. Mathar_, Dec 08 2010

%t With[{cmps=Partition[Select[Range[200],CompositeQ],5,1]},PowerMod[4,#[[1]]-4,#[[5]]]&/@cmps] (* _Harvey P. Dale_, Dec 06 2020 *)

%Y Cf. A000302, A002808.

%K nonn,less

%O 1,2

%A _Juri-Stepan Gerasimov_, Dec 07 2010