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%I #10 Jul 02 2021 03:49:16
%S 0,2,4,6,7,10,12,14,16,18,18,22,21,26,28,30,31,34,36,38,40,42,40,46,
%T 43,50,52,54,55,58,60,62,61,66,64,70,72,74,71,78,79,82,84,86,88,90,90,
%U 94,96,98,100,102,100,106,108,110,112,114,108,118,111,122,124
%N Greatest residue of x^n (mod 2n+1), x=0..2n.
%C If 2n+1 is prime, a(n) = 2n. But there exists nonprime numbers of the form 2n+1 such that a(n) = 2n, for example n = 0, 7, 13, 17, 19, 25, 27, 31, 37, 42, …
%H Amiram Eldar, <a href="/A198033/b198033.txt">Table of n, a(n) for n = 0..10000</a>
%e a(10) = 18 because x^10 == 0, 1, 4, 7, 9, 15, 16, 18 (mod 21) => 18 is the greatest residue.
%t Table[Max[Union[PowerMod[Range[0,2*n],n,2*n+1]]],{n,0,100}]
%Y Cf. A196082, A198020, A198032.
%K nonn
%O 0,2
%A _Michel Lagneau_, Oct 20 2011
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