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 A219019 Smallest number such that k^n - 1 contains n distinct prime divisors. 0
 3, 4, 7, 8, 16, 11, 79, 44, 81, 91, 1024, 47 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE a(3) = 7 is the smallest number of the set  {k(i)} = {7, 9, 13, 15, 19, 21,....} where k(i)^2 - 1 contains 3 primes distinct divisors; MAPLE with(numtheory) :for n from 1 to 10 do:ii:=0:for k from 1 to 10^10 while(ii=0) do:x:=k^n-1:y:=factorset(x):n1:=nops(y):if n1=n then ii:=1: printf ( "%d %d \n", n, k): else fi:od:od: MATHEMATICA L = {}; Do[n = 1; While[Length[FactorInteger[n^k - 1]] != k, n++];  Print@AppendTo[L, n], {k, 15}] (* Giovanni Resta, Nov 10 2012 *) CROSSREFS Cf. A001221. Sequence in context: A112062 A037013 A050069 * A306612 A117587 A244930 Adjacent sequences:  A219016 A219017 A219018 * A219020 A219021 A219022 KEYWORD nonn,hard AUTHOR Michel Lagneau, Nov 09 2012 STATUS approved

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Last modified September 22 13:48 EDT 2021. Contains 347607 sequences. (Running on oeis4.)