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A071852 Smallest k such that 2^k + 1 has exactly n distinct prime factors. 0
1, 5, 14, 18, 30, 42, 99, 114, 78, 90, 175, 150, 324, 210, 315, 234, 270, 585, 405, 765, 390, 450, 510, 1150, 690, 630, 930, 858, 810, 1155, 966, 1386 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(33) > 1500; a(34) = 1365; a(35) = 1350; a(38) = 1170; a(41) = 1530. - Max Alekseyev, Oct 14 2012

LINKS

Table of n, a(n) for n=1..32.

FORMULA

a(n) = min (k : A046799(k) = n ).

MATHEMATICA

For[n = 1, n < 15, n++, k := 1; While[Not[Length[FactorInteger[2^k + 1]] == n], k++ ]; Print[k]] (* Stefan Steinerberger, Apr 09 2006 *)

PROG

(PARI) for(n=1, 10, s=1; while(abs(omega(2^s+1)-n)>0, s++); print1(s, ", "))

CROSSREFS

Sequence in context: A053782 A296692 A102884 * A275809 A227793 A022139

Adjacent sequences:  A071849 A071850 A071851 * A071853 A071854 A071855

KEYWORD

more,nonn

AUTHOR

Benoit Cloitre, Jun 09 2002

EXTENSIONS

175 and 150 from Erich Friedman, Aug 08 2005

a(13)-a(23) from Donovan Johnson, Apr 22 2008

a(24)-a(32) from Max Alekseyev, Oct 14 2012

STATUS

approved

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Last modified October 20 07:33 EDT 2019. Contains 328252 sequences. (Running on oeis4.)