A049095 Numbers k such that 2^k + 1 is squarefree.

0, 1, 2, 4, 5, 6, 7, 8, 11, 12, 13, 14, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 28, 29, 31, 32, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 46, 47, 48, 49, 52, 53, 54, 56, 58, 59, 60, 61, 62, 64, 65, 66, 67, 71, 72, 73, 74, 76, 77, 79, 80, 82, 83, 84, 85, 86, 88, 89, 91, 92, 94, 95

Offset: 1

Author

Labos Elemer

Keywords

• nonn

Examples

			8 is in the sequence because 2^8 + 1 = 257 is prime, hence it is squarefree.
9 is not in the sequence because 2^9 + 1 = 513 is divisible by a square, 9.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000 (calculated from the b-file at A049096)

Crossrefs

Complement of A049096.

Programs

Mathematica

Select[Range[0,95], SquareFreeQ[2^# + 1] &] (* Michael De Vlieger, Jun 29 2017 *)

PARI

isok(n) = issquarefree(2^n + 1); \\ Michel Marcus, Dec 18 2013

Extensions

0 prepended by Jianing Song, May 28 2024