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A108846 Palindromic primes in which all internal digits are 2.

%I A108846 #20 Feb 05 2023 15:15:02
%S A108846 727,929,72227,3222223,9222229,322222223,722222227,9222222222229,
%T A108846 72222222222222222222222222227,
%U A108846 72222222222222222222222222222222222222222222222222222222222222227
%N A108846 Palindromic primes in which all internal digits are 2.
%C A108846 a(14) has 1525 digits. - _Michael S. Branicky_, Jan 27 2023
%H A108846 Michael S. Branicky, <a href="/A108846/b108846.txt">Table of n, a(n) for n = 1..13</a>
%t A108846 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 *)
%o A108846 (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",")) ) ) }
%o A108846 (Python)
%o A108846 from sympy import isprime
%o A108846 from itertools import count, islice
%o A108846 def agen(): yield from (t for i in count(1) for f in "1379" if isprime(t:=int(f + "2"*i + f)))
%o A108846 print(list(islice(agen(), 10))) # _Michael S. Branicky_, Jan 27 2023
%Y A108846 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).
%K A108846 easy,nonn,base
%O A108846 1,1
%A A108846 _Cino Hilliard_, Jul 11 2005
%E A108846 Name changed by _Arkadiusz Wesolowski_, Sep 07 2011