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%I #10 Sep 08 2022 08:45:50
%S 3,7,47,4447,4444444447,44444444444444444447,
%T 44444444444444444444444447
%N Primes of form (4*10^n+23)/9.
%C a(9) has 1310 digits. - _Bruno Berselli_, Jul 26 2012
%H Vincenzo Librandi, <a href="/A173771/b173771.txt">Table of n, a(n) for n = 1..8</a>
%t Select[Table[(4*10^n+23)/9,{n,0,100}],PrimeQ] (* _Vincenzo Librandi_, Jul 26 2012 *)
%o (Magma) [a: n in [0..100] | IsPrime(a) where a is (4*10^n+23)div 9 ]; // _Vincenzo Librandi_, Jul 26 2012
%Y Cf. A173772
%Y Equals 3 followed by A092480 (primes of the form 40*R_n + 7). - _Klaus Brockhaus_ and _R. J. Mathar_, Feb 27 2010
%Y Cf. A056682.
%K nonn
%O 1,1
%A _Vincenzo Librandi_, Feb 24 2010