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A117204 Squarefree positive integers n such that (2n+1) is also squarefree. 3
1, 2, 3, 5, 6, 7, 10, 11, 14, 15, 17, 19, 21, 23, 26, 29, 30, 33, 34, 35, 38, 39, 41, 42, 43, 46, 47, 51, 53, 55, 57, 59, 61, 65, 66, 69, 70, 71, 74, 77, 78, 79, 82, 83, 86, 89, 91, 93 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

COMMENTS

2*a(n) + 1 = A117203(n)

EXAMPLE

10 and 2*10 +1 = 21 are both squarefree, so 10 is in the sequence.

MATHEMATICA

sfQ[n_]:=SquareFreeQ[n]&&SquareFreeQ[2n+1]; Select [Range[200], sfQ] (* From Harvey P. Dale, Mar 12 2011 *)

CROSSREFS

Cf. A005117, A117203, A117206.

Cf. A005384, A111153.

Sequence in context: A166158 A137313 A028805 * A117344 A129127 A078135

Adjacent sequences:  A117201 A117202 A117203 * A117205 A117206 A117207

KEYWORD

nonn

AUTHOR

Leroy Quet Mar 02 2006

EXTENSIONS

More terms from Jonathan Vos Post (jvospost3(AT)gmail.com), Mar 03 2006

Corrected and extended by Harvey P. Dale, Mar 12 2011

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Last modified February 15 18:46 EST 2012. Contains 205836 sequences.