A270344 - OEIS

A270344

Least squarefree number that has runs of exactly n nonsquarefree numbers directly preceding and succeeding it.

2, 17, 26, 2526, 5876126, 8061827, 8996188226, 5295909711327

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OFFSET

0,1

COMMENTS

The sequence appears to be monotone increasing, but the Mathematica implementation does not assume that.

Only a(0) and a(7) differ from A268330 in the numbers computed so far.

LINKS

Table of n, a(n) for n=0..7.

MATHEMATICA

(* computes a(n), 1 <= n <= 5 *)

sfRun[n_]:=Module[{i=n}, While[SquareFreeQ[i], i++]; i-n]

nsfRun[n_]:=Module[{i=n}, While[!SquareFreeQ[i], i++]; i-n]

a270344[{low_, high_}]:=Module[{i, next, r, s, list=Table[{}, 5]}, For[i=low, i<=high, i+=next, r=nsfRun[i]; If[r==0, next=sfRun[i], s=nsfRun[i+r+1]; If[r==s, If[list[[r]]=={}, list[[r]]={i, i+r, i+2r}]; next=2r+2, next=r+1]]]; list]

Map[#[[2]]&, a270344[{0, 10000000}]]]] (* data *)

CROSSREFS

Cf. A268330.

Sequence in context: A340048 A164275 A284646 * A300134 A171605 A018759

Adjacent sequences: A270341 A270342 A270343 * A270345 A270346 A270347

KEYWORD

nonn,more

AUTHOR

Hartmut F. W. Hoft, Mar 15 2016

EXTENSIONS

a(7) from Giovanni Resta, Apr 11 2016

STATUS

approved