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%I
%S 43,4993,49993,499999993,499999999999993,49999999999999993,
%T 4999999999999999999999993,
%U 49999999999999999999999999999999999999999999999999999999999993
%N Primes of the form 5*10^n-7.
%C Primes such that the left-most digit is 4, the right-most digit is 3, and all inner digits are 9.
%H Makoto Kamada, <a href="http://homepage2.nifty.com/m_kamada/math/49993.htm">Factorizations of 499...993</a>.
%F a(n) = 5*10^A103002(n) - 7.
%t Select[Table[FromDigits[Join[PadRight[{4},n+1,9],{3}]],{n,0, 150}],PrimeQ] (* From Harvey P. Dale, Feb 01 2012 *)
%o (PARI) n10np9(n,d) = { local(x,y,k); for(x=1,n, for(k=1,8, y=10^(x+1)*k+(10^x-1)*10+k-1; if(isprime(y),print1(y",")) ) ) }
%o (MAGMA)[a: n in [1..250]|IsPrime(a) where a is (5*10^n-7)] - _Vincenzo Librandi_, Dec 11 2010
%o (PARI) for(n=4,99,if(ispseudoprime(t=10^n/2-7),print1(t", "))) \\ _Charles R Greathouse IV_, Feb 01 2012
%Y Cf. A103002.
%K easy,nonn,base,changed
%O 1,1
%A Cino Hilliard (hillcino368(AT)gmail.com), Jul 11 2005
%E Edited by _Ray Chandler_, Feb 03 2012
%E Comments amended by Harvey P. Dale, Feb 03 2012
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