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

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A117206 Squarefree positive integers n such that (2n-1) is also squarefree. 2
1, 2, 3, 6, 7, 10, 11, 15, 17, 19, 21, 22, 26, 29, 30, 31, 33, 34, 35, 37, 39, 42, 43, 46, 47, 51, 53, 55, 57, 58, 62, 65, 66, 67, 69, 70, 71, 73, 78, 79, 82, 83, 87, 89, 91, 93, 94, 97, 101, 102, 103, 105, 106, 107, 109, 110, 111, 114, 115, 118, 119, 127, 129, 130, 133 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

2*a(n) -1 = A117205(n)

LINKS

Table of n, a(n) for n=1..65.

EXAMPLE

10 and 2*10 -1 = 19 are both squarefree, so 10 is in the sequence.

MAPLE

with(numtheory): a:=proc(n) if abs(mobius(n))>0 and abs(mobius(2*n-1))>0 then n else fi end: seq(a(n), n=1..160); - Emeric Deutsch, Mar 08 2006

MATHEMATICA

Select[Range[200], And@@SquareFreeQ/@{#, 2#-1}&] (* Harvey P. Dale, Dec 17 2012 *)

CROSSREFS

Cf. A005117, A117204, A117205.

Sequence in context: A226115 A073170 A014689 * A026443 A204323 A278965

Adjacent sequences:  A117203 A117204 A117205 * A117207 A117208 A117209

KEYWORD

nonn

AUTHOR

Leroy Quet, Mar 02 2006

EXTENSIONS

More terms from Emeric Deutsch, Mar 08 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 4 23:10 EST 2016. Contains 278755 sequences.