

A185343


Least number k such that k*p+1 divides 2^p+1 where p is prime(n), or 0 if no such number exists.


0



2, 0, 2, 6, 62, 210, 2570, 9198, 121574, 2, 23091222, 48, 2, 68186767614, 6, 2, 48, 12600235023025650, 109368, 794502, 24, 2550476412689091085878, 6, 2, 10, 8367330694575771627040945250, 4030501264, 6, 955272, 2, 446564785985483547852197647548252246, 8, 8, 32424, 8
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OFFSET

1,1


COMMENTS

Akin to A186283 except for 2^p+1 and restricted to primes.
The larger terms of this sequence occur for the primes p > 3 in sequence A000978. These large terms are (2^p2)/(3p).


LINKS

Table of n, a(n) for n=1..35.


EXAMPLE

2^3+1 = 9 has no factor of the form k*3+1, so a(primepi(3)) = a(2) = 0.
2^29+1 = 536870913 has factor 2*29+1=59, so a(primepi(29)) = a(10) = 2.


MATHEMATICA

Table[q = First /@ FactorInteger[2^p + 1]; s = Select[q, Mod[#1, p] == 1 &, 1]; If[s == {}, 0, (s[[1]]  1)/p], {p, Prime[Range[30]]}]


CROSSREFS

Cf. A098268 , A186283.
Sequence in context: A242840 A081081 A111111 * A161014 A344768 A235712
Adjacent sequences: A185340 A185341 A185342 * A185344 A185345 A185346


KEYWORD

easy,nonn


AUTHOR

Bill McEachen, Feb 26 2011


STATUS

approved



