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.

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

Offset

1,2

Comments

Also numbers n such that (88*10^n-61)/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(n-1) + 1, for n>1.

Example

For n=0, (88*10^n-61)/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^n-61)/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