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A069977 Numbers n such that n and n+2 are squarefree. 2
1, 3, 5, 11, 13, 15, 17, 19, 21, 29, 31, 33, 35, 37, 39, 41, 51, 53, 55, 57, 59, 65, 67, 69, 71, 77, 83, 85, 87, 89, 91, 93, 95, 101, 103, 105, 107, 109, 111, 113, 127, 129, 131, 137, 139, 141, 143, 149, 155, 157, 159, 161, 163, 165, 177, 179, 181, 183, 185, 191, 193 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

f[n_] := Union[ Transpose[ FactorInteger[n]] [[ -1]]] [[ -1]]; Select[ Range[200], f[ # ] < 2 && f[ # + 2] < 2 & ]

SequencePosition[Table[If[SquareFreeQ[n], 1, 0], {n, 200}], {1, _, 1}][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 06 2017 *)

PROG

(PARI) is(n)=n%2 && issquarefree(n) && issquarefree(n+2) \\ Charles R Greathouse IV, May 15 2016

CROSSREFS

Cf. A007674.

Sequence in context: A115398 A014597 A130603 * A284795 A329629 A302521

Adjacent sequences:  A069974 A069975 A069976 * A069978 A069979 A069980

KEYWORD

nonn

AUTHOR

Sharon Sela (sharonsela(AT)hotmail.com), May 01 2002

EXTENSIONS

Edited and extended by Robert G. Wilson v, May 04 2002

1 prepended by Vladimir Joseph Stephan Orlovsky, Mar 30 2011

STATUS

approved

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Last modified September 24 06:24 EDT 2020. Contains 337317 sequences. (Running on oeis4.)