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A182154 Smallest k >= 2 such that k^(2^n)+1 is the lesser member of a twin prime pair. 0
2, 2, 2, 4, 2, 49592, 7132, 532, 333482, 2226686, 3543554 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

These lesser of twin prime pairs are also generalized Fermat primes, (not possible for greater of twin prime pairs, except for 5).

When extending this sequence, it is useful if the primes b^(2^n)+1 are known in advance (Gallot link). - Jeppe Stig Nielsen, Sep 25 2019

LINKS

Table of n, a(n) for n=0..10.

Yves Gallot, Generalized Fermat Prime Search.

OEIS Wiki, Generalized Fermat numbers.

EXAMPLE

2^(2^4)+1 = 65537 = A001359(861), then a(4) = 2.

MATHEMATICA

Table[k=2; While[!PrimeQ[k^(2^n)+1]||!PrimeQ[k^(2^n +3], k++]; k, {n, 0, 7}]

CROSSREFS

Cf. A056993, A001359.

Sequence in context: A216951 A320305 A064025 * A273875 A054709 A121806

Adjacent sequences:  A182151 A182152 A182153 * A182155 A182156 A182157

KEYWORD

nonn,more,hard

AUTHOR

Manuel Valdivia, Apr 15 2012

EXTENSIONS

a(8)-a(10) from Jeppe Stig Nielsen, Sep 25 2019

Name edited by Felix Fröhlich, Sep 25 2019

STATUS

approved

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Last modified December 2 02:12 EST 2021. Contains 349435 sequences. (Running on oeis4.)