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 A048692 Triangle read by rows in which row n contains first n numbers with exactly n distinct prime factors. 9
 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 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS David A. Corneth, Table of n, a(n) for n = 1..10011 Sean A. Irvine, Java program (github) EXAMPLE 2; 6, 10; 30, 42, 60; 210, 330, 390, 420; ... MATHEMATICA 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 *) CROSSREFS Cf. A002110 (first column). Main diagonal gives A073329. Extending the rows to give a square array, we get A125666. Sequence in context: A342401 A074095 A079855 * A019095 A246349 A026117 Adjacent sequences: A048689 A048690 A048691 * A048693 A048694 A048695 KEYWORD nonn,tabl AUTHOR Amarnath Murthy, Aug 20 2002 EXTENSIONS Edited, corrected and extended by Robert G. Wilson v, Aug 22 2002 More terms from David A. Corneth, Jan 09 2021 STATUS approved

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Last modified February 27 21:03 EST 2024. Contains 370378 sequences. (Running on oeis4.)