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%I #11 Jan 17 2019 13:44:05
%S 31,311,311111,31111111111,311111111111,31111111111111,
%T 31111111111111111111111111111111111,
%U 311111111111111111111111111111111111111111111111,31111111111111111111111111111111111111111111111111111
%N Primes with a 3 followed by 1's.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/31111.htm#prime">Prime numbers of the form 311...11</a>.
%H H. C. Williams, <a href="http://www.jstor.org/stable/2006356">Some primes with interesting digit patterns</a>, Math. Comp. vol 32 no 144 (1978) pp 1306-1310, Table 2, r=3.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%e Digit 3 followed by rep-units of length 1,2,5,10,11,13,34,47,52,77,88,...
%t Select[Table[FromDigits[PadRight[{3},n,1]],{n,2,100}],PrimeQ] (* _Harvey P. Dale_, Nov 18 2012 *)
%o (PARI) for(n=1,200, if(isprime(3*10^n+(10^(n)-1)/9)==1,print1(3*10^n+(10^(n)-1)/9,",")))
%Y Cf. A002275, A056704.
%K nonn,base
%O 1,1
%A _Amarnath Murthy_, Mar 07 2002
%E More terms from _Benoit Cloitre_, Mar 09 2002
%E One additional term from _Harvey P. Dale_, Nov 18 2012
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