A298729 Prime numbers whose decimal expansion includes a substring of seven consecutive 7's.

137777777, 177777773, 177777779, 197777777, 307777777, 347777777, 437777777, 527777777, 547777777, 577777777, 587777777, 647777777, 697777777, 777777701, 777777739, 777777743, 777777751, 777777799, 787777777, 827777777, 947777777, 967777777, 1247777777, 1277777771, 1277777773, 1457777777, 1487777777

Offset: 1

Author

Yohei Furutono, Jan 25 2018

Keywords

• base
• nonn
• less

Crossrefs

Cf. A102764, A167282, A108844, A083978.

Programs

Mathematica

s = {7, 7, 7, 7, 7, 7, 7}; lst = {}; k = 1; While[k < 10001, l = 1; il = 12;
While[l < il, p = FromDigits@ Flatten@ Insert[ IntegerDigits[k, 10, 10], s, l];
  If[PrimeQ@ p, AppendTo[lst, p]]; l++]; k++]; Union@ lst (* Robert G. Wilson v, Feb 08 2018 *)

PARI

is(n) = my(v=vector(7, x, 7), d=digits(n)); for(k=1, #d-6, if([d[k], d[k+1], d[k+2], d[k+3], d[k+4], d[k+5], d[k+6]]==v, return(1))); 0
forprime(p=1, , if(is(p), print1(p, ", "))) \\ Felix Fröhlich, Mar 06 2018