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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
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
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.)