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Pseudo-powers to base 3: numbers k that are not powers of 3 such that k divides 2^k + 1.
2

%I #11 Jul 04 2021 03:23:32

%S 171,513,1539,3249,4617,9747,13203,13851,29241,39609,41553,61731,

%T 87723,97641,118827,124659,185193,250857,263169,292923,354537,356481,

%U 373977,555579,752571,789507,878769,1063611,1069443,1121931,1172889,1666737,1855179,2152089,2257713

%N Pseudo-powers to base 3: numbers k that are not powers of 3 such that k divides 2^k + 1.

%H Amiram Eldar, <a href="/A016057/b016057.txt">Table of n, a(n) for n = 1..1000</a>

%t Do[ If[ PowerMod[ 2, n, n ] + 1 == n, If[ ! IntegerQ[ Log[ 3, n ] ], Print[ n ] ] ], {n, 1, 4* 10^6} ]

%Y Subsequence of A006521.

%K nonn

%O 1,1

%A _Robert G. Wilson v_

%E Offset corrected by _Amiram Eldar_, Jul 04 2021