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 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 (list; graph; refs; listen; history; text; internal format)
 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^p-2)/(3p). LINKS 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

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Last modified August 5 07:54 EDT 2021. Contains 346464 sequences. (Running on oeis4.)