A056244 -id:A056244 - cp's OEIS frontend

A082697 Numbers k such that (4*10^(k-1) - 7)/3 is a plateau prime.

3, 5, 7, 95, 161, 361, 1471, 2899, 3095, 3113, 15699, 17957, 42263, 111033

Offset: 1

Patrick De Geest, Apr 13 2003

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

			k=7 -> (4*10^(7-1) - 7)/3 = 1333331.

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

Patrick De Geest, PDP Reference Table - 131.
Makoto Kamada, Prime numbers of the form 133...331.
Index entries for primes involving repunits.

Cf. A056244, A068645, A082698-A082720.

a(n) = A056244(n+1) + 2.

a(13)=42263 from Patrick De Geest, Oct 03 2004
a(14)=111033 from Ray Chandler, Apr 14 2011
Edited by Ray Chandler, Nov 04 2014

A068645 Primes in which a string of 3's is sandwiched between two 1's.

Original entry on oeis.org

11, 131, 13331, 1333331, 13333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333331

Offset: 1

Amarnath Murthy, Feb 28 2002

a(5) consists of 93 and a(6) consists of 159 3's sandwiched between two 1's. - Sascha Kurz, Mar 26 2002

a(8) has 1471 digits. - Michael S. Branicky, Jan 27 2023

Michael S. Branicky, Table of n, a(n) for n = 1..7
Patrick De Geest, PDP Reference Table - 131.
Makoto Kamada, Prime numbers of the form 133...331.
Index entries for primes involving repunits.

Cf. A056244, A082697.

 Select[Flatten[Table[10*FromDigits[PadRight[{1},n,3]]+1,{n,120}]],PrimeQ] (* Harvey P. Dale, Aug 09 2020 *)

from sympy import isprime
from itertools import count, islice
def agen(): yield from (t for i in count(0) if isprime(t:=int("1" + "3"*i + "1")))
print(list(islice(agen(), 7))) # Michael S. Branicky, Jan 27 2023

More terms from Sascha Kurz, Mar 26 2002

Edited by Ray Chandler, Nov 04 2014

cp's OEIS Frontend

A082697 Numbers k such that (4*10^(k-1) - 7)/3 is a plateau prime.

Views

Author

Keywords

Comments

Examples

References

Links

Crossrefs

Formula

Extensions