

A103106


Numbers n such that 9*10^n + 7*R_n  4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1



0, 6, 15, 36, 45, 447, 1031, 1239, 3492, 6069, 13647, 17238, 56271, 72711, 75381
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OFFSET

1,2


COMMENTS

Also numbers n such that (88*10^n43)/9 is prime.
a(16) > 10^5.  Robert Price, Nov 12 2015


LINKS

Table of n, a(n) for n=1..15.
Makoto Kamada, Prime numbers of the form 977...773.
Index entries for primes involving repunits.


FORMULA

a(n) = A101015(n1) + 1, for n>1.


MATHEMATICA

Do[ If[ PrimeQ[(88*10^n  43)/9], Print[n]], {n, 0, 10000}]


PROG

(PARI) is(n)=isprime(9*10^n + 7*((10^n1)/9)  4) \\ Anders HellstrÃ¶m, Nov 12 2015


CROSSREFS

Cf. A002275, A101015.
Sequence in context: A338057 A191002 A127469 * A272788 A273151 A320941
Adjacent sequences: A103103 A103104 A103105 * A103107 A103108 A103109


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Jan 19 2005


EXTENSIONS

a(11)a(12) from Kamada data by Robert Price, Dec 14 2010
Inserted a(1)=0 and added a(13)a(15) from Robert Price, Nov 12 2015


STATUS

approved



