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 A125958 Least number k > 0 such that (2^k + (2n-1)^k)/(2n+1) is prime. 2
 3, 3, 3, 5, 3, 3, 7, 3, 5, 5, 11, 3, 19, 11, 3, 229, 47, 5, 257, 3, 19, 31, 17, 11, 13, 3, 3, 5, 5, 59, 23, 3, 3, 7, 79, 3, 3373, 3, 3, 7, 13, 7, 7, 3527, 593, 19, 3, 3, 13, 13, 11, 19, 41, 3, 7, 109, 3, 227, 13, 5, 5, 3, 239, 5 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are odd primes. a(38),...,a(43) = {3,3,7,13,7,7}. a(46),...,a(64) = {19,3,3,13,13,11,19,41,3,7,109,11,227,13,5,5,3,239,5}. a(66) = 3. a(68),...,a(72) = {3,7,31,3,7}. a(74),...,a(92) = {3,5,19,17,3,83,3,3,19,19,11,11,61,3,7,7,3,41,29}. a(94) = 5. a(97),a(98) = {19,7}. a(100) = 31. a(n) is currently unknown for n = {37,44,45,65,67,73,93,95,96,99,...}. LINKS MATHEMATICA Do[k = 1; While[ !PrimeQ[(2^k + (2n-1)^k)/(2n+1)], k++ ]; Print[k], {n, 100}] (* Ryan Propper, Mar 29 2007 *) CROSSREFS Cf. A000978 = numbers n such that (2^n + 1)/3 is prime. Cf. A057469 = numbers n such that (2^n + 3^n)/5 is prime. Cf. A082387 = numbers n such that (2^n + 5^n)/7 is prime. Sequence in context: A096918 A075018 A324974 * A247244 A132448 A132450 Adjacent sequences:  A125955 A125956 A125957 * A125959 A125960 A125961 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Feb 06 2007 EXTENSIONS More terms from Ryan Propper, Mar 29 2007 STATUS approved

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Last modified June 16 12:38 EDT 2019. Contains 324152 sequences. (Running on oeis4.)