A088465 Primes whose leftmost decimal digit is 1 and whose other decimal digits are all 7's.

17, 1777, 1777777777, 17777777777777, 1777777777777777777777777777777777777777777, 1777777777777777777777777777777777777777777777777777

Offset

1,1

Comments

In no element of this sequence can the number of 7's be congruent to 2 modulo 3.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..12

Vladislav Avrutin, Prime pyramids

Makoto Kamada, Prime numbers of the form 177...77.

Index entries for primes involving repunits.

Mathematica

Do[ a = 10^n + 7(10^n - 1)/9; If[ PrimeQ[a], Print[a]], {n, 1, 53}] (* Robert G. Wilson v, Dec 05 2003 *)
Select[Table[FromDigits[PadRight[{1}, n, 7]], {n, 0, 60}], PrimeQ] (* Harvey P. Dale, Jun 15 2022 *)

Crossrefs

Cf. A002275, A089147 (number of sevens).

Sequence in context: A055414 A156675 A276808 * A001905 A221322 A135505

Adjacent sequences: A088462 A088463 A088464 * A088466 A088467 A088468

Keyword

base,easy,nonn

Author

Sam Alexander, Nov 12 2003

Status

approved