A270344 - OEIS

%I #18 Apr 11 2016 08:35:37

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

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

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

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

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

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

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

%t 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]

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

%Y Cf. A268330.

%K nonn,more

%O 0,1

%A _Hartmut F. W. Hoft_, Mar 15 2016

%E a(7) from _Giovanni Resta_, Apr 11 2016