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%I #17 Sep 08 2022 08:46:05
%S 188888881,199999991,322222223,355555553,722222227,17333333317,
%T 19555555519,21444444421,27888888827,29111111129,31333333331,
%U 31555555531,31666666631,39444444439,41999999941,43222222243,43666666643,47999999947,49333333349,49555555549
%N Primes of the form XYYYYYYYX, where Y is a single digit.
%H Vincenzo Librandi, <a href="/A228377/b228377.txt">Table of n, a(n) for n = 1..1000</a>
%t f[n_]: = Block[{len = Floor[Log[10, n] + 1]}, Select[10^(7 + len) n + 10^len Table[k (10^7 - 1) / 9, {k, 9}] + n, PrimeQ@#&]]; Array[f, 1000]//Flatten
%o (Magma) m:=7; [p: d in [1..9], n in [1..80 by 2] | IsPrime(p) where p is n*(10^(m+t)+1)+d*10^t*(10^m-1) div 9 where t is #Intseq(n)]; //
%Y Cf. A154270, A214290, A162423, A214702, A214291.
%K nonn,base
%O 1,1
%A _Vincenzo Librandi_, Sep 12 2013
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