A259138 Numbers k such that R_k + 7*10^k + 6 is prime, where R_k = 11...11 is the repunit (A002275) of length k.

0, 10906, 499210

Offset

1,2

Comments

Also, numbers k such that (64*10^k + 53)/9 is prime.

Terms from Kamada data.

Note that Kamada does not recognize k=0 as 13 is a degenerate case of form ABB..BBA.

a(4) > 1.2*10^6.

Links

Table of n, a(n) for n=1..3.

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

Makoto Kamada, Prime numbers of the form 711...117.

Index entries for primes involving repunits.

Example

For k=10906, R_k + 7*10^k + 6 = R_10906 + 7*10^10906 + 6 = 711...117 which is prime.

Mathematica

Select[Range[0, 1200000], PrimeQ[(64*10^#+53)/9] &]

Crossrefs

Cf. A002275.

Sequence in context: A083513 A084277 A307873 * A082710 A240604 A065322

Adjacent sequences: A259135 A259136 A259137 * A259139 A259140 A259141

Keyword

nonn,bref,more,hard

Author

Robert Price, Jun 18 2015

Status

approved