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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

Table of n, a(n) for n=1..3.

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.)