A108841 Palindromic primes in which all internal digits are 4.

1444441, 3444443, 74444444447, 3444444444443, 7444444444444444444444444444447, 1444444444444444444444444444444444444444444444444444444444444444441

Offset

1,1

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

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 *)

Prog

(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

Crossrefs

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

Sequence in context: A259306 A210629 A156621 * A124490 A124491 A205892

Adjacent sequences: A108838 A108839 A108840 * A108842 A108843 A108844

Keyword

nonn,base

Author

Cino Hilliard, Jul 11 2005

Extensions

Name changed by Arkadiusz Wesolowski, Sep 07 2011

Status

approved