

A098960


Numbers n such that 2*10^n + 7*R_n  6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1




OFFSET

1,1


COMMENTS

Also numbers n such that (25*10^n61)/9 is prime.


LINKS

Table of n, a(n) for n=1..10.
Makoto Kamada, Factorizations of 277...771.
Index entries for primes involving repunits.


EXAMPLE

For n = 2 and 6, we get 271 and 2777771 which are primes.


MATHEMATICA

Do[ If[ PrimeQ[(25*10^n  61)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Sequence in context: A213435 A083666 A083126 * A162429 A243324 A018952
Adjacent sequences: A098957 A098958 A098959 * A098961 A098962 A098963


KEYWORD

more,nonn


AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 22 2004


EXTENSIONS

a(6) from Ray Chandler, Nov 04 2004
a(7), a(8) & a(9) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 03 2004
Addition of a(10) from Kamada data by Robert Price, Dec 13 2010


STATUS

approved



