1,1

The next term, a(8), has 111 digits. - Harvey P. Dale, Nov 12 2011

Table of n, a(n) for n=1..7.

Dario Alejandro Alpern, Factorization using the Elliptic Curve Method.

Makoto Kamada, Prime numbers of the form 100...007.

Index entries for primes involving repunits.

1000000000000000000000007 is a prime with 23 zeros between 1 and 7.

Do[ If[ PrimeQ[10^n + 7], Print[10^n + 7]], {n, 100}] (* Robert G. Wilson v, Apr 05 2009 *)

Select[Table[FromDigits[Join[{1}, PadRight[{}, n, 0], {7}]], {n, 0, 120}], PrimeQ] (* Harvey P. Dale, Nov 12 2011 *)

Cf. A088274. - Robert G. Wilson v, Apr 05 2009

Sequence in context: A007682 A125327 A126485 * A080441 A135400 A052254

Adjacent sequences: A159028 A159029 A159030 * A159032 A159033 A159034

nonn

Parthasarathy Nambi, Apr 02 2009

a(7) from Robert G. Wilson v, Apr 05 2009

approved