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%I #11 Jan 17 2019 13:44:06
%S 499,4999,49999,4999999,499999999999999,
%T 4999999999999999999999999999999999999999999999999999999
%N Primes of the form 5*10^n - 1.
%C Equivalently, primes of the form 4*10^n + 9*R_n, where R_n is the repunit (A002275) of length n.
%C If m is in the sequence then m appears at the end of m^3, in fact if n>1 and m=5*10^n-1 then m appears at the end of m^3. - _Farideh Firoozbakht_, Nov 10 2005
%C If n is in the sequence then 4n is a term of A067206. Namely the digits of 4n end in phi(4n) - the proof is easy. - _Farideh Firoozbakht_, Dec 30 2006
%C The next term -- a(7) -- has 211 digits. - _Harvey P. Dale_, Feb 20 2016
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/4/49999.htm#prime">Prime numbers of the form 499...99</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%t Select[Table[FromDigits[PadRight[{4},n,9]],{n,60}],PrimeQ] (* _Harvey P. Dale_, Feb 20 2016 *)
%Y Cf. A056712 (corresponding n).
%Y Cf. A067206.
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Apr 17 2004
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