A102942 Numbers k such that 10^k + 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 8, 26, 44, 167, 185, 3818, 8741, 50795

Offset

1,2

Comments

Also numbers k such that (16*10^k - 43)/9 is prime.

a(11) > 10^5. - Robert Price, Feb 11 2015

Links

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

Makoto Kamada, Prime numbers of the form 177...773.

Index entries for primes involving repunits.

Formula

a(n) = A102027(n) + 1.

Mathematica

Do[ If[ PrimeQ[(16*10^n - 43)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A102027.

Sequence in context: A150673 A242747 A195585 * A212691 A206803 A212527

Adjacent sequences: A102939 A102940 A102941 * A102943 A102944 A102945

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 16 2004

Extensions

a(10) from Robert Price, Feb 11 2015

Status

approved