%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
|