A103096 Numbers n such that 9*10^n + 3*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 1, 2, 3, 4, 15, 27, 71, 86, 105, 242, 250, 448, 539, 784, 814, 1025, 1172, 1353, 3009, 3175, 3682, 6993, 7612, 7780, 9633, 27109, 27735, 28767, 61574

Offset

1,3

Comments

Also numbers n such that (28*10^n+11)/3 is prime.

a(31) > 10^5. - Robert Price, Nov 07 2015

Links

Table of n, a(n) for n=1..30.

Makoto Kamada, Prime numbers of the form 933...337.

Index entries for primes involving repunits.

Formula

a(n) = A101005(n-1) + 1, for n>1.

Example

For n=0, (28*10^n+11)/3 = 13, which is prime.

Mathematica

Do[ If[ PrimeQ[(28*10^n + 11)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101005.

Sequence in context: A135633 A269725 A270929 * A295757 A005645 A362639

Adjacent sequences: A103093 A103094 A103095 * A103097 A103098 A103099

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(26)-a(28) from Kamada data by Robert Price, Dec 14 2010

Inserted a(1)=0 and added a(30) by Robert Price, Nov 07 2015

Status

approved