The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A176241

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A176241

Numbers n such that n-th semiprime-n is prime
(history; published version)

#10 by Harvey P. Dale at Sun Oct 14 15:39:06 EDT 2018

STATUS

editing

approved

#9 by Harvey P. Dale at Sun Oct 14 15:39:04 EDT 2018

LINKS

Harvey P. Dale, <a href="/A176241/b176241.txt">Table of n, a(n) for n = 1..1000</a>

STATUS

approved

editing

#8 by Harvey P. Dale at Sun Oct 14 15:37:55 EDT 2018

STATUS

editing

approved

#7 by Harvey P. Dale at Sun Oct 14 15:37:52 EDT 2018

MATHEMATICA

Module[{nn=1500, sems}, sems=Select[Range[nn], PrimeOmega[#]==2&]; Select[ Thread[ {sems, Range[Length[sems]]}], PrimeQ[#[[1]]-#[[2]]]&]][[All, 2]] (* Harvey P. Dale, Oct 14 2018 *)

STATUS

approved

editing

#6 by Russ Cox at Fri Mar 30 18:52:40 EDT 2012

AUTHOR

_Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), _, Apr 12 2010

Discussion

Fri Mar 30

18:52

OEIS Server: https://oeis.org/edit/global/257

#5 by Russ Cox at Fri Mar 30 17:40:22 EDT 2012

EXTENSIONS

More terms from _R. J. Mathar (mathar(AT)strw.leidenuniv.nl), _, Apr 13 2010

Discussion

Fri Mar 30

17:40

OEIS Server: https://oeis.org/edit/global/190

#4 by T. D. Noe at Tue Apr 12 14:28:46 EDT 2011

STATUS

proposed

approved

#3 by T. D. Noe at Tue Apr 12 14:28:41 EDT 2011

COMMENTS

Or, numbers n such that A175708(n) is prime . [Zak Seidov, Apr 12 2011]

CROSSREFS

Cf. A175708, A176240. [Zak Seidov, Apr 12 2011]

#2 by Zak Seidov at Mon Apr 11 21:20:21 EDT 2011

COMMENTS

Or, numbers n such that A175708(n) is prime .[Zak Seidov, Apr 12 2011]

CROSSREFS

Cf. A175708, A176240. [Zak Seidov, Apr 12 2011]

STATUS

approved

proposed

#1 by N. J. A. Sloane at Tue Jun 01 03:00:00 EDT 2010

NAME

Numbers n such that n-th semiprime-n is prime

DATA

1, 20, 21, 32, 33, 34, 35, 44, 45, 54, 56, 66, 67, 86, 90, 106, 107, 108, 122, 130, 134, 140, 141, 147, 154, 155, 156, 169, 170, 172, 182, 189, 190, 210, 211, 212, 220, 224, 225, 226, 242, 248, 249, 256, 279, 280, 281, 312, 316, 318, 321, 324, 329, 338, 344

OFFSET

1,2

EXAMPLE

a(1)=1 because A001358(1)-1=4-1=3=prime.

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Apr 12 2010

EXTENSIONS

More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 13 2010

STATUS

approved