

A103105


Numbers n such that 9*10^n + 7*R_n  6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1



0, 2, 4, 41, 53, 64, 197, 238, 784, 3914, 4436, 12538, 19036
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OFFSET

1,2


COMMENTS

Also numbers n such that (88*10^n61)/9 is prime.
a(14) > 10^5.  Robert Price, Nov 10 2015


LINKS

Table of n, a(n) for n=1..13.
Makoto Kamada, Prime numbers of the form 977...771.
Index entries for primes involving repunits.


FORMULA

a(n) = A101014(n1) + 1, for n>1.


EXAMPLE

For n=0, (88*10^n61)/9 = 3 which is prime.


MATHEMATICA

Do[ If[ PrimeQ[(88*10^n  61)/9], Print[n]], {n, 0, 10000}]


PROG

(PARI) for(n=0, 1e3, if(ispseudoprime((88*10^n61)/9), print1(n, ", "))) \\ Altug Alkan, Nov 11 2015


CROSSREFS

Cf. A002275, A101014.
Sequence in context: A292700 A012676 A184245 * A018312 A009547 A215921
Adjacent sequences: A103102 A103103 A103104 * A103106 A103107 A103108


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Jan 19 2005


EXTENSIONS

a(12)a(13) from Kamada data by Robert Price, Dec 14 2010
Inserted a(1)=0 by Robert Price, Nov 10 2015


STATUS

approved



