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 A303448 Numbers m such that both m and (m-1)/2 are Fermat pseudoprimes base 2 (A001567). 8
 19781763, 46912496118443, 192153584101141163 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms below 2^65. Terms a(2) and a(3) are of the form (2^(2k+1)+1)/3 = A007583(k). Terms A007583(k) belong to this sequence for k in A303009. Correspondingly, a(4) <= A007583(A303009(3)) = (2^83+1)/3 = 3223802185639011132549803. If a(n) is not divisible by 3, then it also belongs to A175625. LINKS FORMULA a(n) = 2*A303447(n) + 1. CROSSREFS Numbers (a(n)-1)/2 are listed in A303447. Subsequence of A006970 and A300193. Cf. A175625, A175942, A298758. Sequence in context: A172767 A122557 A284101 * A251513 A103123 A107618 Adjacent sequences:  A303445 A303446 A303447 * A303449 A303450 A303451 KEYWORD bref,hard,more,nonn AUTHOR Max Alekseyev, Apr 24 2018 EXTENSIONS a(1) from Amiram Eldar, Jan 26 2018 STATUS approved

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Last modified April 3 15:51 EDT 2020. Contains 333197 sequences. (Running on oeis4.)