login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A117205 Odd squarefree positive integers n such that (n+1)/2 is also squarefree. 2
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; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..59.

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, Mar 07 2006

MATHEMATICA

Select[Range[1, 301, 2], And@@(SquareFreeQ/@{#, (#+1)/2})&] (* Harvey P. Dale, Jul 30 2013 *)

CROSSREFS

Cf. A005117, A117203, A117206.

Sequence in context: A066587 A047621 A239636 * A147992 A166089 A136208

Adjacent sequences:  A117202 A117203 A117204 * A117206 A117207 A117208

KEYWORD

nonn

AUTHOR

Leroy Quet, Mar 02 2006

EXTENSIONS

More terms from Emeric Deutsch, Mar 07 2006

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 23 20:32 EDT 2019. Contains 325264 sequences. (Running on oeis4.)