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A244673 Numbers k that divide 2^k + 4.

%I A244673 #48 Jan 16 2023 19:47:02
%S A244673 1,2,3,4,20,260,740,2132,2180,5252,43364,49268,49737,80660,130052,
%T A244673 293620,542852,661412,717027,865460,1564180,2185220,2192132,2816372,
%U A244673 3784916,4377620,4427540,5722004,6307652,6919460,8765252,9084452,9498260,9723611,11346260,12208820,12220132
%N A244673 Numbers k that divide 2^k + 4.
%H A244673 Jens Kruse Andersen, <a href="/A244673/b244673.txt">Table of n, a(n) for n = 1..100</a>
%H A244673 OEIS Wiki, <a href="/wiki/2^n mod n">2^n mod n</a>
%e A244673 2^2 + 4 = 8 is divisible by 2. Thus 2 is a term of this sequence.
%e A244673 2^3 + 4 = 12 is divisible by 3. Thus 3 is a term of this sequence.
%e A244673 2^4 + 4 = 20 is divisible by 4. Thus 4 is a term of this sequence.
%p A244673 A244673:=n->`if`(type((2^n+4)/n, integer), n, NULL): seq(A244673(n), n=1..10^5); # _Wesley Ivan Hurt_, Jul 15 2014
%p A244673 Alternative:
%p A244673 select(n -> 4 + 2&^n mod n = 0, [$1..10^5]); # _Robert Israel_, Jul 15 2014
%t A244673 Select[Range[1000], Mod[2^# + 4, #] == 0 &] (* _Alonso del Arte_, Jul 14 2014 *)
%t A244673 Join[{1,2,3},Select[Range[1223*10^4],PowerMod[2,#,#]==#-4&]] (* _Harvey P. Dale_, Jan 16 2023 *)
%o A244673 (PARI) for(n=1, 10^8, if(Mod(2,n)^n+4==0, print1(n, ", "))) \\ _Jens Kruse Andersen_, Jul 15 2014
%Y A244673 The odd terms form A115976.
%Y A244673 Cf. A015921, A140504.
%K A244673 nonn
%O A244673 1,2
%A A244673 _Derek Orr_, Jul 14 2014