A068689 -id:A068689 - cp's OEIS frontend

A108847 Palindromic primes in which all internal digits are 8.

181, 383, 787, 78887, 9888889, 188888881, 3888888888883, 188888888888881, 3888888888888888888888888888883, 18888888888888888888888888888888888888881

Offset: 1

Cino Hilliard, Jul 11 2005

a(27) has 1065 digits. - Michael S. Branicky, Jan 27 2023

Michael S. Branicky, Table of n, a(n) for n = 1..26

Similar sequences for digit d: A108845 (d=1), A108846 (d=2), A108841 (d=4), A108842 (d=5), A108843 (d=6), A108844 (d=7), A108848 (d=9).

n10np1(n,d) = { local(x,y,k); for(x=1,n, for(k=1,9, y=10^(x+1)*k+floor(10^x*d/9)*10+k; if(isprime(y),print1(y",")) ) ) }

from sympy import isprime
from itertools import count, islice
def agen(): yield from (t for i in count(1) for f in "1379" if isprime(t:=int(f + "8"*i + f)))
print(list(islice(agen(), 10))) # Michael S. Branicky, Jan 27 2023

Name changed by Arkadiusz Wesolowski, Sep 07 2011

One comment moved to A068689 by Michel Marcus, Jan 28 2023

A068688 Primes which are a sandwich of numbers made of only one digit between two 7's.

Original entry on oeis.org

727, 757, 787, 797, 72227, 75557, 76667, 78887, 79997, 7666667, 722222227, 74444444447, 75555555557, 755555555555555555557, 75555555555555555555557, 72222222222222222222222222227, 79999999999999999999999999997, 7444444444444444444444444444447

Offset: 1

Amarnath Murthy, Mar 02 2002

The middle digit is never 0, 1, 3, or 7. - Harvey P. Dale, May 05 2018

a(40) has 1213 digits. - Michael S. Branicky, Jan 28 2023

Harvey P. Dale, Table of n, a(n) for n = 1..39

Cf. A068685, A068687, A068689.

Select[Flatten[Table[10FromDigits[PadRight[{7},n,i]]+7,{n,2,100},{i,9}]],PrimeQ] (* Harvey P. Dale, May 05 2018 *)

from sympy import isprime
from itertools import count, islice
def agen(): yield from (t for i in count(1) for m in "0123456789" if isprime(t:=int("7" + m*i + "7")))
print(list(islice(agen(), 30))) # Michael S. Branicky, Jan 28 2023

More terms from Sascha Kurz, Mar 17 2002

cp's OEIS Frontend

A108847 Palindromic primes in which all internal digits are 8.

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