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%I #14 Mar 21 2023 08:26:45
%S 3,7,3,5,3,11,11,113,151,19,61,53,89,5,307,19,19,491,3,11,271,41,251,
%T 271,359,3,19,79,233,5,7,13,11,5,29,71,139,127,139,2003,5,743,673,593,
%U 383,653,661,251,6389,2833,223,163,37,709,131,41,2203,941,2707,13,1283
%N a(n) = least odd prime p such that (p^(P(n))-1)/(p-1) is prime with P(i) = i-th prime, n>1.
%C All primes certified using PRIMO.
%e (3^3-1)/2=26/2=13 prime so for P(2) a(2)=3.
%t a = {}; Do[ p1 = Prime[n]; k = 2; While[p2 = Prime[k]; ! PrimeQ[(p2^p1 - 1)/(p2 - 1)], k++ ]; AppendTo[a, p2];, {n, 2, 62}]; a (* _Ray Chandler_, Jan 27 2005 *)
%t f[n_] := Block[{P = Prime[n], k = 2}, While[p = Prime[k]; !PrimeQ[(p^P - 1)/(p - 1)], k++ ]; Prime[ k]]; Table[ f[n], {n, 2, 62}] (* _Robert G. Wilson v_, Jan 27 2005 *)
%o (PARI) a(n) = my(p=3, q=prime(n)); while (!ispseudoprime((p^q-1)/(p-1)), p=nextprime(p+1)); p; \\ _Michel Marcus_, Mar 21 2023
%K nonn
%O 2,1
%A _Pierre CAMI_, Jan 26 2005
%E Extended by _Ray Chandler_ and _Robert G. Wilson v_, Jan 27 2005