A093174 - OEIS

A093174

Primes of the form 40*R_k + 1, where R_k is the repunit (A002275) of length k.

41, 4441, 44444444441, 4444444444444444444444444441, 4444444444444444444444444444444444444444444444444444441, 4444444444444444444444444444444444444444444444444444444444444444444444444444444444444444444441

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OFFSET

1,1

COMMENTS

Primes of the form (4*10^k - 31)/9. - Vincenzo Librandi, Nov 16 2010

The next term (a(7)) has 475 digits. (* Harvey P. Dale, May 06 2026 *)

LINKS

Table of n, a(n) for n=1..6.

Makoto Kamada, Prime numbers of the form 44...441.

Index entries for primes involving repunits

MATHEMATICA

Select[Table[FromDigits[PadLeft[{1}, n, 4]], {n, 100}], PrimeQ] (* Harvey P. Dale, May 06 2026 *)

CROSSREFS

Cf. A056681 (corresponding k), A173768.

Sequence in context: A282054 A107690 A068815 * A280677 A209104 A233079

Adjacent sequences: A093171 A093172 A093173 * A093175 A093176 A093177

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Mar 27 2004

EXTENSIONS

Edited by N. J. A. Sloane, Feb 26 2010

STATUS

approved