A014661 Numbers that do not divide 2^k + 1 for any k>0.

2, 4, 6, 7, 8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 23, 24, 26, 28, 30, 31, 32, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 47, 48, 49, 50, 51, 52, 54, 55, 56, 58, 60, 62, 63, 64, 66, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 82, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• nice

Comments

A195470(a(n)) = 0 for n > 1. [Reinhard Zumkeller, Sep 21 2011]

References

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

Links

• T. D. Noe, Table of n, a(n) for n=1..1000

Crossrefs

Cf. A014657.

Cf. A000051.

Programs

Haskell

import Data.List (elemIndices)
a014661 n = a014661_list !! (n-1)
a014661_list = 2 : map (+ 1) (elemIndices 0 $ map a195470 [1..])
-- Reinhard Zumkeller, Sep 21 2011

Mathematica

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 *)
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 *)

Extensions

More terms from Henry Bottomley, May 19 2000