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A270344
Least squarefree number that has runs of exactly n nonsquarefree numbers directly preceding and succeeding it.
6
2, 17, 26, 2526, 5876126, 8061827, 8996188226, 5295909711327
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.
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
KEYWORD
nonn,more
AUTHOR
Hartmut F. W. Hoft, Mar 15 2016
EXTENSIONS
a(7) from Giovanni Resta, Apr 11 2016
STATUS
approved