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A303447 Numbers m such that both m and 2m+1 are Fermat pseudoprimes base 2 (A001567). 5
9890881, 23456248059221, 96076792050570581 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

No other terms below 2^64.

Terms a(2) and a(3) are of the form (4^k-1)/3=A002450(k). Terms A002450(k) belong to this sequence for k in A303009. Correspondingly, a(4) <= A002450(A303009(3)) = (4^41-1)/3 = 1611901092819505566274901.

LINKS

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

CROSSREFS

Numbers 2*a(n)+1 are listed in A303448.

Subsequence of A006970.

Cf. A298758, A300193.

Sequence in context: A034606 A233839 A059044 * A107617 A234980 A179737

Adjacent sequences:  A303444 A303445 A303446 * A303448 A303449 A303450

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 1 13:39 EDT 2020. Contains 333159 sequences. (Running on oeis4.)