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 A127958 Numbers x such that 1 + Sum_{k=1..n} 2^(2k-1) is not prime for n=1,2,...,x. 11
 4, 7, 10, 12, 13, 14, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 84, 85 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers x such that 1 + Sum_{k=1..n} 2^(2k-1) is prime for n=1,2,...,x gives A127936. LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 MATHEMATICA a = {}; Do[If[PrimeQ[1 + Sum[2^(2n - 1), {n, 1, x}]] == False, AppendTo[a, x]], {x, 1, 1000}]; a PROG (PARI) isok(x) = !isprime(1+sum(k=1, x, 2^(2*k-1))); \\ Michel Marcus, May 09 2018 CROSSREFS Cf. A000979, A000978, A124400, A126614, A127955, A127957, A127936. Sequence in context: A087298 A237707 A211642 * A000414 A025357 A222949 Adjacent sequences:  A127955 A127956 A127957 * A127959 A127960 A127961 KEYWORD nonn AUTHOR Artur Jasinski, Feb 09 2007 STATUS approved

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Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)