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 A049095 Numbers k such that 2^k + 1 is squarefree. 4
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE 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. MATHEMATICA Select[Range@ 95, SquareFreeQ[2^# + 1] &] (* Michael De Vlieger, Jun 29 2017 *) PROG (PARI) isok(n) = issquarefree(2^n + 1); \\ Michel Marcus, Dec 18 2013 CROSSREFS Complement of A049096. Sequence in context: A276706 A271396 A070110 * A324583 A101742 A194831 Adjacent sequences:  A049092 A049093 A049094 * A049096 A049097 A049098 KEYWORD nonn AUTHOR STATUS approved

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Last modified January 23 04:16 EST 2020. Contains 331168 sequences. (Running on oeis4.)