A259128 Numbers k such that R_k + 3*10^k + 2 is prime, where R_k = 11...11 is the repunit (A002275) of length k.

0, 2, 12, 14, 30, 104, 126, 342, 600, 9824

Offset

1,2

Comments

Also, numbers k such that (28*10^k + 17)/9 is prime.

Terms from Kamada data.

Note that Kamada does not recognize k=0 as 5 is a degenerate case of form ABB..BBA.

a(11) > 10^5.

Links

Table of n, a(n) for n=1..10.

Makoto Kamada, Near-repdigit numbers of the form ABB...BBA.

Makoto Kamada, Prime numbers of the form 311...113.

Index entries for primes involving repunits.

Example

For k=2, R_2 + 3*10^k + 2 = 11 300 + 2 = 313 which is prime.

Mathematica

Select[Range[0, 100000], PrimeQ[(28*10^#+17)/9] &]

Prog

(Magma) [n: n in [0..400] | IsPrime((28*10^n+17) div 9)]; // Vincenzo Librandi, Jun 19 2015

Crossrefs

Cf. A002275.

Sequence in context: A232768 A022368 A076484 * A280942 A270119 A340016

Adjacent sequences: A259125 A259126 A259127 * A259129 A259130 A259131

Keyword

nonn,more,hard

Author

Robert Price, Jun 18 2015

Status

approved