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%I #7 Nov 15 2020 16:26:50
%S 7,17,37,47,67,97,227,337,557,887,997,1117,4447,5557,8887,11117,
%T 333337,555557,666667,888887,11111117,66666667,222222227,666666667,
%U 888888887,4444444447,5555555557,66666666667,888888888887,222222222222227
%N Primes of the form identical digits followed by a 7.
%H Vincenzo Librandi, <a href="/A090147/b090147.txt">Table of n, a(n) for n = 1..68</a>
%t Select[ FromDigits /@ Flatten[ Table[ PadLeft[{7}, i, # ] & /@ {1, 2, 3, 4, 5, 6, 7, 8, 9}, {i, 2, 18}], 1], PrimeQ[ # ] &]
%t Select[Union[Flatten[Table[FromDigits[PadLeft[{7},n,d]],{n,15},{d,9}]]],PrimeQ] (* _Harvey P. Dale_, Nov 15 2020 *)
%K nonn,base
%O 1,1
%A _Robert G. Wilson v_, Nov 22 2003
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