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 A137990 Least prime p of the form c*3^n+1 with c not divisible by 3. 1
 2, 7, 19, 109, 163, 487, 1459, 17497, 52489, 39367, 472393, 4960117, 5314411, 102036673, 19131877, 57395629, 86093443, 258280327, 3874204891, 23245229341, 90656394427, 585779779369, 251048476873, 9790890598009, 4518872583697 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) is also the least prime such that 3^(n+1), but not 3^(n+2), divides 2^(a(n)-1)-1. LINKS Table of n, a(n) for n=0..24. Carlos Rivera, Puzzle 1129 OEIS A137990, The Prime Puzzles & Problems Connection. EXAMPLE 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. CROSSREFS Cf. A005109, A057775. Sequence in context: A080873 A126162 A054423 * A056650 A182169 A170869 Adjacent sequences: A137987 A137988 A137989 * A137991 A137992 A137993 KEYWORD easy,nonn AUTHOR Andrew V. Sutherland, May 01 2008 STATUS approved

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Last modified September 22 07:58 EDT 2023. Contains 365519 sequences. (Running on oeis4.)