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 A074477 Largest prime factor of 3^n - 1. 5
 2, 2, 13, 5, 11, 13, 1093, 41, 757, 61, 3851, 73, 797161, 1093, 4561, 193, 34511, 757, 363889, 1181, 368089, 3851, 1001523179, 6481, 391151, 797161, 8209, 16493, 20381027, 4561, 4404047, 21523361, 2413941289, 34511, 2664097031, 530713 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Amiram Eldar, Table of n, a(n) for n = 1..660 (terms 1..100 from Vincenzo Librandi) S. S. Wagstaff, Jr., The Cunningham Project FORMULA a(n) = A006530(A024023(n)). - Michel Marcus, Jul 18 2015 EXAMPLE 3^7 - 1 = 2186 = 2*1093, so a(7) = 1093. MAPLE A074477 := proc(n)         A006530( 3^n-1) ; end proc: # R. J. Mathar, Jul 18 2015 # alternative: a:= n-> max(seq(i[1], i=ifactors(3^n-1)[2])): seq(a(n), n=1..40);  # Alois P. Heinz, Jul 18 2015 MATHEMATICA Table[FactorInteger[3^n - 1] [[-1, 1]], {n, 40}] (* Vincenzo Librandi, Aug 23 2013 *) PROG (PARI) for(n=1, 40, v=factor(3^n-1); print1(v[matsize(v)[1], 1], ", ")) (MAGMA) [Maximum(PrimeDivisors(3^n-1)): n in [1..40]]; // Vincenzo Librandi, Aug 23 2013 CROSSREFS Cf. A006530 (largest prime factor), A024023 (3^n-1). Cf. A074476 (largest prime factor of 3^n + 1), A005420 (largest prime factor of 2^n - 1), A074479 (largest prime factor of 5^n - 1). Sequence in context: A130718 A268528 A173331 * A141575 A306738 A151352 Adjacent sequences:  A074474 A074475 A074476 * A074478 A074479 A074480 KEYWORD nonn AUTHOR Rick L. Shepherd, Aug 23 2002 STATUS approved

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Last modified December 1 16:55 EST 2020. Contains 338846 sequences. (Running on oeis4.)