The On-Line Encyclopedia of Integer Sequences (OEIS)

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A152617

Smallest number m such that m has exactly n distinct prime factors and sigma(m) has exactly n distinct prime factors.
(history; published version)

#5 by Russ Cox at Fri Mar 30 17:35:01 EDT 2012

AUTHOR

_Donovan Johnson (donovan.johnson(AT)yahoo.com), _, Dec 13 2008

EXTENSIONS

a(12) from _Donovan Johnson (donovan.johnson(AT)yahoo.com), _, Jul 13 2011

Discussion

Fri Mar 30

17:35

OEIS Server: https://oeis.org/edit/global/163

#4 by T. D. Noe at Wed Jul 13 20:15:07 EDT 2011

STATUS

proposed

approved

#3 by Donovan Johnson at Wed Jul 13 20:12:35 EDT 2011

STATUS

editing

proposed

#2 by Donovan Johnson at Wed Jul 13 20:11:29 EDT 2011

DATA

2, 6, 60, 1140, 22230, 778050, 28787850, 1237877550, 82937795850, 6054459097050, 802693813972050, 126022928793611850

COMMENTS

a(1213) <= 20541737393358731550. a(14) <= 1260229287936118503553720569051060558150. - Donovan Johnson, Jul 13 2011

EXTENSIONS

a(12) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jul 13 2011

STATUS

approved

editing

#1 by N. J. A. Sloane at Fri Jan 09 03:00:00 EST 2009

NAME

Smallest number m such that m has exactly n distinct prime factors and sigma(m) has exactly n distinct prime factors.

DATA

2, 6, 60, 1140, 22230, 778050, 28787850, 1237877550, 82937795850, 6054459097050, 802693813972050

OFFSET

1,1

COMMENTS

a(12) <= 126022928793611850.

EXAMPLE

a(9) = 82937795850 = 2*3^2*5^2*7*13*19*37*43*67 (9 distinct prime factors). Sigma(82937795850) = 307906959360 = 2^11*3*5*7*11*13*17*19*31 (9 distinct prime factors).

CROSSREFS

Cf. A000203, A001221.

KEYWORD

nonn,new

AUTHOR

Donovan Johnson (donovan.johnson(AT)yahoo.com), Dec 13 2008

STATUS

approved