A103053 - OEIS

A103053

Numbers n such that 7*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 4, 12, 13, 15, 36, 40, 90, 837, 2424, 2427, 2443, 15925, 16212

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OFFSET

1,2

COMMENTS

Also numbers n such that (65*10^n+7)/9 is prime.

a(15) > 10^5. - Robert Price, Sep 22 2015

LINKS

FORMULA

a(n) = A101134(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(65*10^n + 7)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

KEYWORD

more,nonn

AUTHOR

EXTENSIONS

a(13)-a(14) from Kamada data by Robert Price, Dec 14 2010

STATUS

approved