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A048692
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Triangle read by rows in which row n contains first n numbers with exactly n distinct prime factors.
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9
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2, 6, 10, 30, 42, 60, 210, 330, 390, 420, 2310, 2730, 3570, 3990, 4290, 30030, 39270, 43890, 46410, 51870, 53130, 510510, 570570, 690690, 746130, 870870, 881790, 903210, 9699690, 11741730, 13123110, 14804790, 15825810, 16546530, 17160990, 17687670, 223092870, 281291010, 300690390, 340510170, 358888530, 363993630, 380570190, 397687290, 406816410
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OFFSET
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1,1
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LINKS
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EXAMPLE
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2;
6, 10;
30, 42, 60;
210, 330, 390, 420;
...
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MATHEMATICA
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f[n_] := Flatten[Table[ # [[1]]] & /@ FactorInteger[n]]; (* for n=7 *) Take[ Select[ Range[10^7], Length[f[ # ]] == 7 & ], 7]
Module[{nn=8, dpf=Table[{n, PrimeNu[n]}, {n, 2 10^7}]}, Flatten[Table[Select[dpf, #[[2]]==n&, n], {n, nn}], 1][[All, 1]]] (* The program generates the first 36 terms of the sequence. *) (* Harvey P. Dale, Sep 09 2022 *)
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CROSSREFS
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Extending the rows to give a square array, we get A125666.
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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