A102978 Numbers n such that 3*10^n + 8*R_n - 7 is a prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 19, 30, 40, 42, 45, 70, 307, 538, 1609, 1668, 1674, 4492, 4935, 6112, 12819, 14079, 16020, 23005, 50997, 82870

Offset

1,2

Comments

Also numbers n such that (35*10^n-71)/9 is a prime.

a(23) > 10^5. - Robert Price, May 20 2015

Links

Table of n, a(n) for n=1..22.

Makoto Kamada, Prime numbers of the form 388...881.

Index entries for primes involving repunits.

Formula

a(n) = A101844(n) + 1.

Mathematica

Do[ If[ PrimeQ[(35*10^n - 71)/9], Print[n]], {n, 0, 10000}]

Crossrefs

Cf. A002275, A101844.

Sequence in context: A108137 A250027 A339545 * A218537 A236969 A222590

Adjacent sequences: A102975 A102976 A102977 * A102979 A102980 A102981

Keyword

more,nonn

Author

Robert G. Wilson v, Dec 17 2004

Extensions

Addition of a(17)-a(20) from Kamada data by Robert Price, Dec 10 2010

a(21)-a(22) from Robert Price, May 20 2015

Status

approved