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%I #11 Dec 16 2019 16:54:42
%S 1,3,7,9,13,27,31,37,39,49,51,57,63,67,73,79,81,91,93,97,99,103,109,
%T 117,123,129,151,153,163,171,181,187,193,201,213,217,223,229,231,237,
%U 249,259,277,279,283,289,291,297,301,303,307,319,321,327,361,367,373
%N Digit '1' concatenated with a(n) is a prime.
%H Seiichi Manyama, <a href="/A032664/b032664.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[400],PrimeQ[10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, Dec 16 2019 *)
%K nonn,base
%O 1,2
%A _Patrick De Geest_, May 15 1998
%E Edited by _Charles R Greathouse IV_, Apr 24 2010
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