A048692 Triangle read by rows in which row n contains first n numbers with exactly n distinct prime factors.

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

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