A093940 Primes of the form 4*10^k + 7*R_k, where R_k is the repunit (A002275) of length k.

47, 47777, 47777777777777, 47777777777777777777777777, 4777777777777777777777777777777777777

Offset

1,1

Comments

The next term has 358 digits. - Harvey P. Dale, Nov 13 2013

Links

Table of n, a(n) for n=1..5.

Makoto Kamada, Prime numbers of the form 477...77.

Index entries for primes involving repunits.

Mathematica

Select[Table[FromDigits[PadRight[{4}, n, 7]], {n, 500}], PrimeQ] (* Harvey P. Dale, Nov 13 2013 *)

Crossrefs

Cf. A002275, A056708 (corresponding k).

Sequence in context: A287225 A033520 A210818 * A237512 A224468 A353697

Adjacent sequences: A093937 A093938 A093939 * A093941 A093942 A093943

Keyword

nonn

Author

Rick L. Shepherd, Apr 17 2004

Status

approved