A093938 Primes of the form 2*10^k + 7*R_k, where R_k is the repunit (A002275) of length k.

2, 277, 2777, 2777777777, 2777777777777777, 2777777777777777777, 2777777777777777777777777777777777777, 2777777777777777777777777777777777777777777777777777777777777777

Offset

1,1

Links

Table of n, a(n) for n=1..8.

Makoto Kamada, Prime numbers of the form 277...77.

Index entries for primes involving repunits

Mathematica

Select[FromDigits/@Table[PadRight[{2}, n, 7], {n, 200}], PrimeQ] (* Harvey P. Dale, May 14 2011 *)

Crossrefs

Cf. A002275, A056702 (corresponding k).

Sequence in context: A200168 A215043 A119553 * A172374 A231041 A080296

Adjacent sequences: A093935 A093936 A093937 * A093939 A093940 A093941

Keyword

nonn

Author

Rick L. Shepherd, Apr 17 2004

Status

approved