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

Author

Amarnath Murthy, Aug 20 2002

Keywords

• nonn
• tabl

Examples

			    2;
    6,  10;
   30,  42,  60;
  210, 330, 390, 420;
  ...
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..10011
• Sean A. Irvine, Java program (github)

Crossrefs

Cf. A002110 (first column).

Main diagonal gives A073329.

Extending the rows to give a square array, we get A125666.

Programs

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 *)

Extensions

Edited, corrected and extended by Robert G. Wilson v, Aug 22 2002

More terms from David A. Corneth, Jan 09 2021