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A264840 Consider the sequence {3k, k >= 1}, and write down the numbers of consecutive terms that are squarefree. 2
2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is a (1,2)-sequence (every term is either 1 or 2), since out of every three consecutive multiples of 3 at least one is not squarefree (it is divisible by 9).

LINKS

Peter J. C. Moses, Table of n, a(n) for n = 1..1000

EXAMPLE

The multiples of 3 are 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, .... The squarefree ones are (3,6), (15), (21), (30,33), .... So a(1)=2, a(2)=1, a(3)=1, a(4)=2, ....

MATHEMATICA

Map[Count[#, True]&, DeleteCases[Split[Map[SquareFreeQ[3#]&, Range[400]]], {___, False, ___}]] (* Peter J. C. Moses, Nov 26 2015 *)

CROSSREFS

Cf. A005117, A261034, A264843.

Sequence in context: A126207 A276711 A191322 * A308188 A046219 A088978

Adjacent sequences:  A264837 A264838 A264839 * A264841 A264842 A264843

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Nov 26 2015

EXTENSIONS

More terms from Peter J. C. Moses, Nov 26 2015

STATUS

approved

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Last modified September 27 21:12 EDT 2021. Contains 347698 sequences. (Running on oeis4.)