A056683 -id:A056683 - cp's OEIS frontend

A093402 Primes of the form 40*R_k + 9, where R_k is the repunit (A002275) of length k.

449, 44449, 444449, 444444444444444444444444444444444444444444444449, 444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444449

Offset: 1

Rick L. Shepherd, Mar 28 2004

nonn

Primes of the form (4*10^k + 41)/9. - Vincenzo Librandi, Nov 16 2010

Makoto Kamada, Prime numbers of the form 44...449.
Index entries for primes involving repunits

Cf. A056683 (corresponding k).

Select[Table[FromDigits[PadLeft[{9},n,4]],{n,120}],PrimeQ] (* Harvey P. Dale, May 21 2011 *)

A099414 Numbers k such that 4*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

0, 3, 5, 6, 48, 108, 245, 1044, 20208, 52740, 89189, 130080, 183657, 197061, 348453

Offset: 1

Robert G. Wilson v, Oct 14 2004

Also numbers k such that (4*10^k + 41)/9 is prime.

a(12) > 10^5. - Robert Price, Nov 09 2014

Makoto Kamada, Prime numbers of the form 44...449.
Index entries for primes involving repunits

Cf. A002275, A056683.

[n: n in [0..300] | IsPrime((4*10^n+41) div 9)]; // Vincenzo Librandi Nov 10 2014

Do[ If[ PrimeQ[ 4(10^n - 1)/9 + 5], Print[n]], {n, 5000}]

a(n) = A056683(n-1) + 1.

a(9)-a(11) from Robert Price, Nov 09 2014

a(12)-a(15) from Kamada data by Tyler Busby, Apr 29 2024

cp's OEIS Frontend

A093402 Primes of the form 40*R_k + 9, where R_k is the repunit (A002275) of length k.

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