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A117205 Odd squarefree positive integers n such that (n+1)/2 is also squarefree. +0
3
1, 3, 5, 11, 13, 19, 21, 29, 33, 37, 41, 43, 51, 57, 59, 61, 65, 67, 69, 73, 77, 83, 85, 91, 93, 101, 105, 109, 113, 115, 123, 129, 131, 133, 137, 139, 141, 145, 155, 157, 163, 165, 173, 177, 181, 185, 187, 193, 201, 203, 205, 209, 211, 213, 217, 219, 221, 227, 229 (list; graph; listen)
OFFSET

1,2

COMMENT

(a(n)+1)/2 = A117206(n)

EXAMPLE

21 and (21+1)/2 = 11 are both squarefree, so 21 is in the sequence.

MAPLE

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=1..300); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 07 2006

CROSSREFS

Cf. A005117, A117203, A117206.

Sequence in context: A020578 A066587 A047621 this_sequence A136208 A045405 A059311

Adjacent sequences: A117202 A117203 A117204 this_sequence A117206 A117207 A117208

KEYWORD

nonn

AUTHOR

Leroy Quet (qq-quet(AT)mindspring.com), Mar 02 2006

EXTENSIONS

More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 07 2006

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Last modified November 18 20:14 EST 2008. Contains 147244 sequences.


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