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%I #11 Sep 08 2022 08:45:18
%S 1,17,23,37,41,47,73,103,137,149,157,173,181,187,193,197,199,221,239,
%T 253,257,317,319,337,349,373,379,401,403,421,451,461,481,491,509,521,
%U 527,557,569,587,599,617,643,667,701,703,713,719,751,773,781,787,793
%N Numbers n such that the string 1113n is the decimal expansion of a prime number.
%C 11 and 13 are twin primes.
%H Harvey P. Dale, <a href="/A107644/b107644.txt">Table of n, a(n) for n = 1..1000</a>
%e n=1: 11131 is prime.
%e n=47: 111347 is prime.
%e n=149: 1113149 is prime.
%t Select[Range[800],PrimeQ[1113*10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, Sep 26 2016 *)
%o (Magma) [ n: n in [1..800] | IsPrime(Seqint(Intseq(n) cat [3, 1, 1, 1])) ];
%K nonn,base
%O 1,2
%A _Parthasarathy Nambi_, Jun 09 2005
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