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A172186 Numbers k such that k, k+1 and 2*k+1 are squarefree. 7
1, 2, 5, 6, 10, 14, 21, 29, 30, 33, 34, 38, 41, 42, 46, 57, 61, 65, 66, 69, 70, 77, 78, 82, 86, 93, 101, 102, 105, 106, 109, 110, 113, 114, 118, 129, 133, 138, 141, 142, 145, 154, 158, 165, 173, 177, 178, 182, 185, 186, 190, 194, 201, 205, 209, 210, 213, 214, 217, 218 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This sequence is similar to A007674. For terms in A007674 which lack in this sequence see A172187.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = (A179017(n)-1)/2.

MATHEMATICA

Select[Range[250], And @@ SquareFreeQ /@ {#, # + 1, 2 # + 1} &]  (* Harvey P. Dale, Mar 11 2011 *)

CROSSREFS

Cf. A007674, A172187, A179017.

Sequence in context: A348565 A316946 A005984 * A178761 A274037 A227975

Adjacent sequences:  A172183 A172184 A172185 * A172187 A172188 A172189

KEYWORD

nonn

AUTHOR

Artur Jasinski, Jan 28 2010

STATUS

approved

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Last modified November 28 06:42 EST 2021. Contains 349401 sequences. (Running on oeis4.)