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A087858 Lesser of twin primes p such that 2^p-1 is prime. 1
3, 5, 17, 107, 521 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

Are there any further terms?

LINKS

Table of n, a(n) for n=2..6.

PROG

(PARI) twopm1(n) = { sr=0; forprime(x=2, n, y=2^x-1; if(isprime(x+2), y2=2^(x+2)-1, y2=0); if(isprime(y) && isprime(x+2), print1(x", "); sr+=1.0/y; sr+=1.0/y2; ) ); }

CROSSREFS

Sequence in context: A302199 A174722 A176131 * A191222 A084723 A288376

Adjacent sequences:  A087855 A087856 A087857 * A087859 A087860 A087861

KEYWORD

easy,nonn

AUTHOR

Cino Hilliard, Oct 25 2003

STATUS

approved

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Last modified June 19 18:02 EDT 2021. Contains 345144 sequences. (Running on oeis4.)