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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
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.
FORMULA
a(n) = 2*A303447(n) + 1.
CROSSREFS
Numbers (a(n)-1)/2 are listed in A303447.
Subsequence of A006970 and A300193.
Sequence in context: A172767 A122557 A284101 * A251513 A103123 A107618
KEYWORD
bref,hard,more,nonn
AUTHOR
Max Alekseyev, Apr 24 2018
EXTENSIONS
a(1) from Amiram Eldar, Jan 26 2018
STATUS
approved