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 A117706 Numbers k such that 6^k - k^6 is prime. 10
 1, 7, 13, 35, 53, 115, 145, 307, 10163 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(9) found by Donovan Johnson. Comment from Donovan Johnson: A117705 and A117706 are both Fermat probable prime to four bases. They have also passed a Miller-Rabin primality test in five randomly chosen bases. I checked the n values up to 70000 for A117705 and n values up to 60000 for A117706. No additional primes or probable primes were found. The actual primes are listed in A243114. - M. F. Hasler, Aug 20 2014 From the Lifchitz link: 100193 and 114433 are also in this sequence. - Robert Price, Mar 27 2019 LINKS Henri Lifchitz and Renaud Lifchitz, PRP Records. EXAMPLE a(2)=7 because 6^7 - 7^6 = 162287 is prime. MATHEMATICA Do[If[PrimeQ[(6^n-n^6)], Print[n]], {n, 1, 3000}] PROG (PARI) for(x=1, 1e5, ispseudoprime(p=6^x-x^6)&&print1(x", ")) \\ M. F. Hasler, Aug 20 2014 CROSSREFS Cf. A128448. Sequence in context: A060983 A001001 A067692 * A066673 A307762 A290947 Adjacent sequences:  A117703 A117704 A117705 * A117707 A117708 A117709 KEYWORD hard,more,nonn AUTHOR Mohammed Bouayoun (Mohammed.Bouayoun(AT)sanef.com), Apr 13 2006, Jan 08 2008 STATUS approved

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Last modified July 31 13:25 EDT 2021. Contains 346373 sequences. (Running on oeis4.)