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A229627 a(n) is the smallest prime m such that 2*m^k-1 is prime for k = 1, 2, ..., n. 2
2, 2, 3, 92581, 385939, 464938699, 24137752519 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The prime number 2 in the definition is used because 2 is the only prime p such that for more than one prime q, p*q^k -1 can be prime.

LINKS

Table of n, a(n) for n=1..7.

MATHEMATICA

a[1]=2; a[n_]:=a[n]=(For[m=PrimePi[a[n-1]], Union[Table[PrimeQ[2 Prime[m]^k-1], {k, n}]]!={True}, m++]; Prime[m])]

PROG

(PARI) a(n)=forprime(m=2, , for(k=1, n, if(!ispseudoprime(2*m^k-1), next(2))); return(m)) \\ Charles R Greathouse IV, Oct 01 2013

CROSSREFS

Cf. A229626.

Sequence in context: A094877 A006560 A088251 * A140839 A320299 A292943

Adjacent sequences:  A229624 A229625 A229626 * A229628 A229629 A229630

KEYWORD

nonn,more

AUTHOR

Farideh Firoozbakht, Sep 27 2013

EXTENSIONS

a(7) from Giovanni Resta, Oct 01 2013

STATUS

approved

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Last modified January 16 21:37 EST 2019. Contains 319206 sequences. (Running on oeis4.)