login
A103050
Numbers n such that 7*10^n + R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 7, 133, 938, 17666, 20864, 56756
OFFSET
1,2
COMMENTS
Also numbers n such that (64*10^n+17)/9 is prime.
a(8) > 10^5. - Robert Price, Sep 18 2015
FORMULA
a(n) = A101131(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(64*10^n + 17)/9], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=isprime((64*10^n + 17)/9) \\ Anders Hellström, Sep 18 2015
CROSSREFS
Sequence in context: A305955 A377006 A051832 * A110111 A245318 A370782
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(5)-a(6) from Kamada data by Robert Price, Dec 14 2010
a(7) from Robert Price, Sep 18 2015
STATUS
approved