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 A108837 Primes of the form 5*10^n-7. 0

%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.

%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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