cp's OEIS Frontend

A195470 Number of numbers k with 0 <= k < n such that 2^k + 1 is multiple of n.

%I A195470 #39 Aug 03 2014 14:01:33
%S A195470 1,1,1,0,1,0,0,0,1,0,1,0,1,0,0,0,2,0,1,0,0,0,0,0,1,0,1,0,1,0,0,0,3,0,
%T A195470 0,0,1,0,0,0,2,0,3,0,0,0,0,0,0,0,0,0,1,0,0,0,3,0,1,0,1,0,0,0,5,0,1,0,
%U A195470 0,0,0,0,0,0,0,0,0,0,0,0,1,0,1,0,0,0
%N A195470 Number of numbers k with 0 <= k < n such that 2^k + 1 is multiple of n.
%C A195470 a(A014657(n)) > 0; for n > 1: a(A014661(n)) = 0.
%H A195470 Reinhard Zumkeller, <a href="/A195470/b195470.txt">Table of n, a(n) for n = 1..10000</a>
%e A195470 a(1)=#{0}=1, (2^0 + 1) mod 1;
%e A195470 a(17) = #{4, 12} = 2, (2^4 + 1) mod 17 = (2^12 + 1) mod 17 = 0;
%e A195470 a(18) = #{} = 0;
%e A195470 a(19) = #{9} = 1, (2^9 + 1) mod 19 = 0.
%t A195470 nn = 100; pwrs = 2^Range[0, nn] + 1; Table[cnt = 0; Do[If[Mod[pwrs[[i]], n] == 0, cnt++], {i, n}]; cnt, {n, nn}] (* _T. D. Noe_, Sep 30 2011 *)
%o A195470 (Haskell)
%o A195470 a195470 n = length $ filter ((== 0) . (`mod` n)) $
%o A195470                        take (fromInteger n) a000051_list
%Y A195470 Cf. A000051, A195610.
%K A195470 nonn
%O A195470 1,17
%A A195470 _Reinhard Zumkeller_, Sep 21 2011