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A303448
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Numbers m such that both m and (m-1)/2 are Fermat pseudoprimes base 2 (A001567).
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8
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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FORMULA
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CROSSREFS
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Numbers (a(n)-1)/2 are listed in A303447.
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KEYWORD
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bref,hard,more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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