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A103041
Numbers n such that 6*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
2, 5, 8, 17, 20, 65, 83, 90, 108, 252, 335, 1488, 6356, 65712, 96798
OFFSET
1,1
COMMENTS
Also numbers n such that (59*10^n+31)/9 is prime.
a(16) > 10^5. - Robert Price, Sep 13 2015
FORMULA
a(n) = A101534(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(59*10^n + 31)/9], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=isprime(6*10^n + 5*(10^n-1)/9 + 4) \\ Anders Hellström, Sep 13 2015
CROSSREFS
Sequence in context: A055236 A345430 A214124 * A216307 A176223 A006827
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 18 2005
EXTENSIONS
a(14)-a(15) from Robert Price, Sep 13 2015
STATUS
approved