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%I #17 Sep 15 2019 11:08:20
%S 41,4111,41111111111111,41111111111111111111111111,
%T 4111111111111111111111111111111111111111111111111111111111111111111111111
%N Primes with a 4 followed by 1's.
%C The next term a(6) has 109 digits and is too large to be displayed here.
%H Harvey P. Dale, <a href="/A068815/b068815.txt">Table of n, a(n) for n = 1..10</a>
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/41111.htm#prime">Prime numbers of the form 411...11</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t Select[Table[FromDigits[PadRight[{4},n,1]],{n,1000}],PrimeQ] (* _Harvey P. Dale_, Sep 15 2019 *)
%o (PARI) for(n=1,200, if(isprime(4*10^n+(10^(n)-1)/9)==1,print1(4*10^n+(10^(n)-1)/9,",")))
%Y Cf. A002275, A056706 (corresponding values of n).
%K nonn,base
%O 1,1
%A _Amarnath Murthy_, Mar 07 2002
%E More terms from _Benoit Cloitre_, Mar 09 2002