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A137990 Least prime p of the form c*3^n+1 with c not divisible by 3. 1

%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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Last modified December 3 15:26 EST 2023. Contains 367540 sequences. (Running on oeis4.)