A103065 Numbers k such that 7*10^k + 6*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

1, 2, 3, 6, 8, 18, 19, 21, 32, 48, 65, 72, 99, 120, 201, 308, 717, 968, 1344, 2132, 3567, 3968, 8327, 10598, 12465, 15875, 18895, 28611, 29418, 83693, 114962, 145040, 256654, 262324, 295581

Offset

1,2

Comments

Also numbers k such that (23*10^k+7)/3 is prime.

a(36) > 3*10^5. - Robert Price, Jul 13 2023

Links

Table of n, a(n) for n=1..35.

Makoto Kamada, Prime numbers of the form 766...669.

Index entries for primes involving repunits.

Formula

a(n) = A101150(n) + 1.

Mathematica

Do[ If[ PrimeQ[(23*10^n + 7)/3], Print[n]], {n, 0, 10000}]

Prog

(PARI) for(n=1, 10^5, if(isprime((23*10^n+7)/3), print1(n", "))) \\ Altug Alkan, Oct 08 2015

Crossrefs

Cf. A002275, A101150.

Sequence in context: A329128 A368687 A330442 * A281142 A110448 A005508

Adjacent sequences: A103062 A103063 A103064 * A103066 A103067 A103068

Keyword

more,nonn

Author

Robert G. Wilson v, Jan 19 2005

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(28)-a(29) from Kamada data by Robert Price, Dec 14 2010

a(30) from Robert Price, Oct 08 2015

a(31)-a(35) from Robert Price, Jul 13 2023

Status

approved