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Search: id:A117203
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| A117203 |
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Odd squarefree positive integers n such that (n-1)/2 is also squarefree. |
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+0
4
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| 3, 5, 7, 11, 13, 15, 21, 23, 29, 31, 35, 39, 43, 47, 53, 59, 61, 67, 69, 71, 77, 79, 83, 85, 87, 93, 95, 103, 107, 111, 115, 119, 123, 131, 133, 139, 141, 143, 149, 155, 157, 159, 165, 167, 173, 179, 183, 187, 191, 195, 203, 205, 211, 213, 215, 219, 221, 223, 227
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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(a(n)-1)/2 = A117204(n)
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EXAMPLE
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21 and (21-1)/2 = 10 are both squarefree, so 21 is in the sequence.
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MAPLE
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with(numtheory): a:=proc(n) if n mod 2 =1 and abs(mobius(n))>0 and abs(mobius((n-1)/2))>0 then n else fi end: seq(a(n), n=2..300); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 07 2006
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MATHEMATICA
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fQ[n_] := Max @@ Last /@ FactorInteger@n < 2; Select[ 2Range@113 + 1, fQ@# && fQ[(# - 1)/2] &] (* Robert G. Wilson v *)
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PROGRAM
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(PARI) for (i=1, 100, if(issquarefree(2*i+1) && issquarefree(i), print1(2*i+1, ", "))) - Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Mar 23 2006
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CROSSREFS
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Cf. A005117, A117204, A117205.
a(n) = 2*A117344(n) + 1.
Sequence in context: A047484 A036991 A091892 this_sequence A081118 A003255 A118749
Adjacent sequences: A117200 A117201 A117202 this_sequence A117204 A117205 A117206
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Mar 02 2006
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu) and Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Mar 07 2006
More terms from Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Mar 23 2006
More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Apr 18 2006
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