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A068685 Primes which are a sandwich of numbers using at most one digit between two 1's.

%I A068685 #13 Jan 28 2023 12:10:55
%S A068685 11,101,131,151,181,191,13331,15551,16661,19991,1333331,1444441,
%T A068685 1777771,188888881,199999991,1666666666661,188888888888881,
%U A068685 16666666666666661,1111111111111111111,1666666666666666661,155555555555555555551,11111111111111111111111
%N A068685 Primes which are a sandwich of numbers using at most one digit between two 1's.
%C A068685 a(47) has 1003 digits. - _Michael S. Branicky_, Jan 28 2023
%H A068685 Michael S. Branicky, <a href="/A068685/b068685.txt">Table of n, a(n) for n = 1..46</a>
%e A068685 11 is a member sandwiching nothing between two 1's. 13331 is a sandwich using 333.
%t A068685 Select[Union[Flatten[Table[FromDigits[Join[{1},PadRight[{},n,i],{1}]], {n,0,20},{i,0,9}]]],PrimeQ] (* _Harvey P. Dale_, Mar 29 2012 *)
%o A068685 (Python)
%o A068685 from sympy import isprime
%o A068685 from itertools import count, islice
%o A068685 def agen(): yield 11; yield from (t for i in count(1) for m in "0123456789" if isprime(t:=int("1" + m*i + "1")))
%o A068685 print(list(islice(agen(), 30))) # _Michael S. Branicky_, Jan 28 2023
%Y A068685 Cf. A068683.
%K A068685 base,nonn
%O A068685 1,1
%A A068685 _Amarnath Murthy_, Mar 02 2002
%E A068685 More terms from _Sascha Kurz_, Mar 17 2002
%E A068685 a(21) and beyond from _Michael S. Branicky_, Jan 28 2023