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A078178 Least k>=2 such that n^k + n - 1 is prime. 3

%I #7 May 24 2020 15:10:59

%S 2,2,2,2,2,3,2,2,2,2,4,2,16,2,2,4,3,2,2,2,7,4,2,3,2,3,2,10,2,2,108,3,

%T 6,2,3,7,2,2,4,2,16,3,2,2,2,20,2,7,2,3,3,2,2,2,2,9,4,2,2,7,8,3,2,2,2,

%U 24,2,6,2,12,4,3,8,6,2,4,3,9,194,3,13,2,8,2,2,3,8,2,10,6,4,2,2,54,2,132,4,10,2

%N Least k>=2 such that n^k + n - 1 is prime.

%C n^a(n) + n - 1 = A078179(n).

%e 7^2+7-1=5*11, but 7^3+7-1=349=A000040(70), therefore a(7)=3.

%t lkp[n_]:=Module[{k=2},While[!PrimeQ[n^k+n-1],k++];k]; Array[lkp,100,2] (* _Harvey P. Dale_, May 24 2020 *)

%o (Haskell)

%o a078178 n = head [k | k <- [2..], a010051'' (n ^ k + n - 1) == 1]

%o -- _Reinhard Zumkeller_, Jul 16 2014

%Y Cf. A076845, A078179.

%Y Cf. A010051.

%K nonn

%O 2,1

%A _Reinhard Zumkeller_, Nov 20 2002

%E More terms from Benoit Cloitre, Nov 20 2002

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)