A103063 Numbers k such that 7*10^k + 6*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 1, 2, 6, 25, 69, 253, 300, 384, 434, 721, 822, 883, 2192, 2649, 3441, 3445, 8028, 11655

Offset

1,3

Comments

Also numbers k such that (23*10^k-17)/3 is prime.

a(20) > 10^5. - Robert Price, Oct 22 2015

Links

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 766...661.

Index entries for primes involving repunits.

Formula

a(n) = A101147(n-1) + 1, for n>1.

Example

For n=0, (23*10^n - 17)/3 = , which is prime.

Mathematica

Do[ If[ PrimeQ[(23*10^n - 17)/3], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101147.

Sequence in context: A294945 A353363 A073545 * A220191 A030228 A066317

Adjacent sequences: A103060 A103061 A103062 * A103064 A103065 A103066

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(19) from Kamada data by Robert Price, Dec 14 2010

a(1)=0 inserted by Robert Price, Oct 22 2015

Status

approved