A108841 Palindromic primes in which all internal digits are 4.

1444441, 3444443, 74444444447, 3444444444443, 7444444444444444444444444444447, 1444444444444444444444444444444444444444444444444444444444444444441

Offset: 1

Author

Cino Hilliard, Jul 11 2005

Keywords

• nonn
• base

Comments

The next term has 121 digits. - Harvey P. Dale, Nov 26 2014

a(10) has 1255 digits, and thus is too big for a b-file. - Robert Israel, Oct 25 2018

Links

• Robert Israel, Table of n, a(n) for n = 1..9

Crossrefs

Similar sequences for digit d: A108845 (d=1), A108846 (d=2), A108842 (d=5), A108843 (d=6), A108844 (d=7), A108847 (d=8).

Programs

Maple

select(isprime, [seq(seq(x*(10^d+1)+40*(10^(d-1)-1)/9,x=1..9,2),d=2..66)]); # Robert Israel, Oct 25 2018

Mathematica

Sort[Select[FromDigits/@Flatten[Table[Join[{n},PadRight[{},i,4],{n}],{n,{1,3,7,9}},{i,150}],1],PrimeQ]] (* Harvey P. Dale, Nov 26 2014 *)

PARI

n10np1(n,d) = { local(x,y,k); for(x=1,n, for(k=1,8, y=10^(x+1)*k+floor(10^x*d/9)*10+k; if(isprime(y),print1(y",")) ) ) }

Python

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 + "4"*i + f)))
print(list(islice(agen(), 9))) # Michael S. Branicky, Jan 27 2023

Extensions

Name changed by Arkadiusz Wesolowski, Sep 07 2011