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Primes p such that there exists at least one x in 2..p-1 with x = order(x) modulo p.
2

%I #7 Feb 11 2024 17:30:57

%S 3,11,13,17,19,29,31,37,41,53,59,61,67,71,73,83,89,97,101,107,131,137,

%T 139,149,163,173,179,181,191,193,197,211,227,233,241,251,269,271,281,

%U 293,307,313,317,337,347,349,373,379,389,401,409,419,421,439,443,449

%N Primes p such that there exists at least one x in 2..p-1 with x = order(x) modulo p.

%e 13 is in the sequence because the order of 3 modulo 13 is 3.

%o (PARI) forprime(p=3, 500, for(x=2, p-1, if(znorder(Mod(x, p))==x, print1(p, ", "); break)))

%K easy,nonn

%O 1,1

%A _Nick Hobson_, Jan 11 2007