A014661 - OEIS

%I #21 Dec 17 2021 00:47:56

%S 2,4,6,7,8,10,12,14,15,16,18,20,21,22,23,24,26,28,30,31,32,34,35,36,

%T 38,39,40,42,44,45,46,47,48,49,50,51,52,54,55,56,58,60,62,63,64,66,68,

%U 69,70,71,72,73,74,75,76,77,78,79,80,82,84,85,86,87,88,89,90,91,92,93,94

%N Numbers that do not divide 2^k + 1 for any k>0.

%C A195470(a(n)) = 0 for n > 1. [_Reinhard Zumkeller_, Sep 21 2011]

%D P. Moree, Appendix to V. Pless et al., Cyclic Self-Dual Z_4 Codes, Finite Fields Applic., vol. 3 pp. 48-69, 1997.

%H T. D. Noe, <a href="/A014661/b014661.txt">Table of n, a(n) for n=1..1000</a>

%t divQ[n_] := For[k = 1, k <= n, k++, If[Divisible[2^k + 1, n], Return[True], If[k == n, Return[False]]]]; Select[Range[100], !divQ[#]& ] (* _Jean-François Alcover_, Jun 18 2012 *)

%t dndQ[n_]:=NoneTrue[2^Range[n]+1,Divisible[#,n]&]; Select[Range[100],dndQ] (* The program uses the NoneTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Feb 10 2015 *)

%o (Haskell)

%o import Data.List (elemIndices)

%o a014661 n = a014661_list !! (n-1)

%o a014661_list = 2 : map (+ 1) (elemIndices 0 $ map a195470 [1..])

%o -- _Reinhard Zumkeller_, Sep 21 2011

%Y Cf. A014657.

%Y Cf. A000051.

%K nonn,nice

%O 1,1

%A _N. J. A. Sloane_

%E More terms from _Henry Bottomley_, May 19 2000