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A116998 a(n) is the smallest number having no fewer distinct prime factors than any predecessor; a(1) = 1. 5
1, 2, 3, 4, 5, 6, 10, 12, 14, 15, 18, 20, 21, 22, 24, 26, 28, 30, 42, 60, 66, 70, 78, 84, 90, 102, 105, 110, 114, 120, 126, 130, 132, 138, 140, 150, 154, 156, 165, 168, 170, 174, 180, 182, 186, 190, 195, 198, 204, 210, 330, 390, 420, 462, 510, 546, 570, 630, 660 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A001221(a(n)) <= A001221(a(n+1));

A002110 is a subsequence.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..2500

MAPLE

a:= proc(n) option remember; local k, t;

      t:= nops(ifactors(a(n-1))[2]);

      for k from 1+a(n-1) while nops(ifactors(k)[2])<t do od; k

    end: a(1):=1:

seq(a(n), n=1..80);  # Alois P. Heinz, Oct 05 2012

MATHEMATICA

a[1] = 1; a[n_] := a[n] = For[nu = PrimeNu[a[n-1]]; k = a[n-1]+1, True, k++, If[PrimeNu[k] >= nu, Return[k]]]; Array[a, 80] (* Jean-Fran├žois Alcover, Apr 11 2017 *)

CROSSREFS

Cf. A029744.

Cf. A001221 (omega), A002110 (primorial numbers).

Sequence in context: A210184 A015853 A018642 * A285614 A078931 A018779

Adjacent sequences:  A116995 A116996 A116997 * A116999 A117000 A117001

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Apr 03 2006

STATUS

approved

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Last modified March 23 10:55 EDT 2019. Contains 321424 sequences. (Running on oeis4.)