

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



