A108846 Palindromic primes in which all internal digits are 2.

727, 929, 72227, 3222223, 9222229, 322222223, 722222227, 9222222222229, 72222222222222222222222222227, 72222222222222222222222222222222222222222222222222222222222222227

Offset

1,1

Comments

a(14) has 1525 digits. - Michael S. Branicky, Jan 27 2023

Links

Michael S. Branicky, Table of n, a(n) for n = 1..13

Mathematica

Select[Flatten[Table[10 FromDigits[PadRight[{d}, n, 2]]+d, {d, {1, 3, 7, 9}}, {n, 2, 70}]], PrimeQ]//Sort (* Harvey P. Dale, Feb 05 2023 *)

Prog

(PARI) 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", ")) ) ) }
(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 + "2"*i + f)))
print(list(islice(agen(), 10))) # Michael S. Branicky, Jan 27 2023

Crossrefs

Similar sequences for digit d: A108845 (d=1), A108841 (d=4), A108842 (d=5), A108843 (d=6), A108844 (d=7), A108847 (d=8), A108848 (d=9).

Sequence in context: A068688 A088283 A123096 * A052234 A103170 A153215

Adjacent sequences: A108843 A108844 A108845 * A108847 A108848 A108849

Keyword

easy,nonn,base

Author

Cino Hilliard, Jul 11 2005

Extensions

Name changed by Arkadiusz Wesolowski, Sep 07 2011

Status

approved