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%I #8 May 15 2023 12:15:00
%S 2,7,19,109,163,487,1459,17497,52489,39367,472393,4960117,5314411,
%T 102036673,19131877,57395629,86093443,258280327,3874204891,
%U 23245229341,90656394427,585779779369,251048476873,9790890598009,4518872583697
%N Least prime p of the form c*3^n+1 with c not divisible by 3.
%C a(n) is also the least prime such that 3^(n+1), but not 3^(n+2), divides 2^(a(n)-1)-1.
%H Carlos Rivera, <a href="https://www.primepuzzles.net/puzzles/puzz_1129.htm">Puzzle 1129 OEIS A137990</a>, The Prime Puzzles & Problems Connection.
%e a(8)=52489 because 52489=8*3^8+1 is prime and no smaller prime p has p-1 divisible by 3^8 but not 3^9.
%Y Cf. A005109, A057775.
%K easy,nonn
%O 0,1
%A _Andrew V. Sutherland_, May 01 2008
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