A103064 Numbers n such that 7*10^n + 6*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 7, 90, 93, 125, 147, 498, 868, 879, 1157, 2958, 3018, 3317, 3822, 6948, 8885, 13092, 33323, 35847, 79492

Offset

1,2

Comments

Also numbers n such that (23*10^n-11)/3 is prime.

a(21) > 10^5. - Robert Price, Oct 14 2015

Links

Table of n, a(n) for n=1..20.

Makoto Kamada, Prime numbers of the form 766...663.

Index entries for primes involving repunits.

Formula

a(n) = A101148(n) + 1.

Mathematica

Do[ If[ PrimeQ[(23*10^n - 11)/3], Print[n]], {n, 0, 10000}]

Prog

(Magma) [n: n in [0..500] | IsPrime((23*10^n-11) div 3)]; // Vincenzo Librandi, Oct 15 2015

Crossrefs

Cf. A002275, A101148.

Sequence in context: A142995 A350937 A200832 * A244849 A355591 A360914

Adjacent sequences: A103061 A103062 A103063 * A103065 A103066 A103067

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

a(17) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(18)-a(19) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(20) from Robert Price, Oct 14 2015

Status

approved