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 A255707 Least number k > 0 such that (2*n-1)^k - 2 is prime, or 0 if no such number exists. 5
 0, 2, 1, 1, 1, 4, 1, 1, 6, 1, 1, 24, 1, 2, 2, 1, 1, 2, 2, 1, 4, 1, 1, 2, 1, 8, 4, 1, 12, 4, 1, 1, 8, 3, 1, 2, 1, 1, 2, 38, 1, 4, 1, 4, 2, 1, 2, 4, 747, 1, 4, 1, 1, 2, 1, 1, 10, 1, 2, 2, 2, 6, 42, 2, 1, 2, 1, 2, 10, 1, 1, 4, 2, 16, 50, 1, 1, 2, 22, 1, 2, 38 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Michel Marcus, Table of n, a(n) for n = 1..152 (terms 1..143 from Robert Price) Carlos Rivera, Puzzle 887. p(n)^c-2 is prime, The Prime Puzzles and Problems Connection. FORMULA a(A098090(n)) = 1. - Michel Marcus, Mar 03 2015 MATHEMATICA lst = {0}; For[n = 2, n ≤ 143, n++, For[k = 1, k >= 1, k++, If[PrimeQ[(2*n - 1)^k - 2], AppendTo[lst, k]; Break[]]]]; lst PROG (PARI) a(n)=if(n==1, return(0)); k=1; while(k, if(ispseudoprime((2*n-1)^k-2), return(k)); k++) vector(50, n, a(n)) \\ Derek Orr, Mar 03 2015 CROSSREFS Cf. A079706, A084712, A084713, A084714, A098090, A138066. Sequence in context: A299203 A329036 A205552 * A260757 A157114 A156786 Adjacent sequences:  A255704 A255705 A255706 * A255708 A255709 A255710 KEYWORD nonn AUTHOR Robert Price, Mar 02 2015 STATUS approved

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Last modified April 15 07:23 EDT 2021. Contains 342975 sequences. (Running on oeis4.)