A056247 -id:A056247 - cp's OEIS frontend

A068647 Primes in which a string of 6's is sandwiched between two 1's.

11, 16661, 1666666666661, 16666666666666661, 1666666666666666661, 1666666666666666666666666666666666661, 16666666666666666666666666666666666666666666666666661

Offset: 1

Amarnath Murthy, Feb 28 2002

nonn

The next term -- a(8) -- has 73 digits. - Harvey P. Dale, Jun 18 2021

			11 is also a member in which a string of 0 6's is there between two one's.

Patrick De Geest, PDP Reference Table - 161.
Makoto Kamada, Prime numbers of the form 166...661.
Index entries for primes involving repunits.

Cf. A068645-A068651, A056247, A082700.

Select[Table[10*FromDigits[PadRight[{1},n,6]]+1,{n,60}],PrimeQ] (* Harvey P. Dale, Jun 18 2021 *)

More terms from Sascha Kurz, Mar 19 2002

Edited by Ray Chandler, Nov 04 2014

A082700 Numbers k such that (15*10^(k-1) - 51)/9 is a plateau prime.

Original entry on oeis.org

5, 13, 17, 19, 37, 53, 73, 101, 6233, 24029, 40223, 66395

Offset: 1

Patrick De Geest, Apr 13 2003

Prime versus probable prime status and proofs are given in the author's table.

			k=13 -> (15*10^(13-1) - 51)/9 = 1666666666661.

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

Patrick De Geest, PDP Reference Table - 161.
Makoto Kamada, Prime numbers of the form 166...661.
Index entries for primes involving repunits.

Cf. A056247, A068647, A082697-A082720.

is(n)=ispseudoprime(2*(10^n-1)/3-5*(10^(n-1)+1)) || ispseudoprime(15*10^(n-1)-51)/9 \\ Charles R Greathouse IV, Feb 07 2013

a(n) = A056247(n+1) + 2.

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

Edited by Ray Chandler, Nov 04 2014

cp's OEIS Frontend

A068647 Primes in which a string of 6's is sandwiched between two 1's.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

Mathematica

Extensions