The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A102368 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A102368

Smallest k>0 such that n^k + 1 is not prime.
(history; published version)

#11 by N. J. A. Sloane at Sun Apr 10 10:16:34 EDT 2016

STATUS

proposed

approved

#10 by Joerg Arndt at Sun Apr 10 10:15:50 EDT 2016

STATUS

editing

proposed

#9 by Harvey P. Dale at Sat Apr 09 11:15:58 EDT 2016

MATHEMATICA

sk[n_]:=Module[{k=1}, While[PrimeQ[n^k+1], k++]; k]; Array[sk, 110, 2] (* Harvey P. Dale, Apr 09 2016 *)

STATUS

approved

editing

#8 by Bruno Berselli at Sun Jun 15 16:59:20 EDT 2014

STATUS

proposed

approved

#7 by Robert Israel at Sun Jun 15 15:07:09 EDT 2014

STATUS

editing

proposed

#6 by Robert Israel at Sun Jun 15 15:06:57 EDT 2014

LINKS

Robert Israel, <a href="/A102368/b102368.txt">Table of n, a(n) for n = 2..10000</a>

MAPLE

A102368:= proc(n)

if n::odd or not isprime(n+1) then 1

elif isprime(n^2+1) then 3 else 2

fi

end proc; # Robert Israel, Jun 15 2014

STATUS

proposed

editing

#5 by Robert Israel at Sun Jun 15 15:03:03 EDT 2014

STATUS

editing

proposed

#4 by Robert Israel at Sun Jun 15 15:02:58 EDT 2014

COMMENTS

Since n + 1 divides n^3 + 1, a(n) <= 3. - Robert Israel, Jun 15 2014

CROSSREFS

Cf. A070689: a(n) = 3.

STATUS

approved

editing

#3 by Russ Cox at Fri Mar 30 18:50:48 EDT 2012

AUTHOR

_Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), _, Feb 22 2005

Discussion

Fri Mar 30

18:50

OEIS Server: https://oeis.org/edit/global/246

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

KEYWORD

nonn,new

nonn

AUTHOR

Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystemsgmail.com), Feb 22 2005