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A073249
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Nonprime squarefree numbers n such that both n-1 and n+1 are not squarefree and not prime.
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4
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26, 51, 55, 91, 161, 170, 235, 249, 295, 305, 339, 341, 362, 377, 413, 415, 451, 485, 489, 530, 551, 559, 579, 595, 629, 638, 649, 651, 665, 667, 685, 687, 703, 721, 723, 737, 749, 849, 851, 874, 917, 926, 949, 951, 955, 962, 989, 1015, 1027, 1057, 1059
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OFFSET
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1,1
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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MATHEMATICA
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npsQ[n_]:=SquareFreeQ[n]&&NoneTrue[n+{1, 0, -1}, PrimeQ]&&NoneTrue[n+{1, -1}, SquareFreeQ]; Select[Range[2000], npsQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 20 2019 *)
Mean/@SequencePosition[Table[Which[CompositeQ[n]&&SquareFreeQ[n], 1, !SquareFreeQ[ n] && CompositeQ[ n], -1, True, 0], {n, 1100}], {-1, 1, -1}] (* Harvey P. Dale, Jun 17 2022 *)
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CROSSREFS
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Cf. A000469, A005117, A073247, A073250, A073251.
Sequence in context: A261932 A324041 A137263 * A044078 A044459 A158060
Adjacent sequences: A073246 A073247 A073248 * A073250 A073251 A073252
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller, Jul 22 2002
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EXTENSIONS
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Corrected by Harvey P. Dale, Jan 20 2019
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STATUS
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approved
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