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A108837
Primes of the form 5*10^n-7.
2
43, 4993, 49993, 499999993, 499999999999993, 49999999999999993, 4999999999999999999999993, 49999999999999999999999999999999999999999999999999999999999993
OFFSET
1,1
COMMENTS
Primes such that the leftmost digit is 4, the rightmost digit is 3, and all inner digits are 9.
FORMULA
a(n) = 5*10^A103002(n) - 7.
MATHEMATICA
Select[Table[FromDigits[Join[PadRight[{4}, n+1, 9], {3}]], {n, 0, 150}], PrimeQ] (* Harvey P. Dale, Feb 01 2012 *)
PROG
(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", ")) ) ) }
(Magma)[a: n in [1..250]|IsPrime(a) where a is (5*10^n-7)] // Vincenzo Librandi, Dec 11 2010
(PARI) for(n=4, 99, if(ispseudoprime(t=10^n/2-7), print1(t", "))) \\ Charles R Greathouse IV, Feb 01 2012
CROSSREFS
Sequence in context: A110704 A060485 A081795 * A091748 A208625 A147522
KEYWORD
easy,nonn,base
AUTHOR
Cino Hilliard, Jul 11 2005
EXTENSIONS
Edited by Ray Chandler, Feb 03 2012
Comments amended by Harvey P. Dale, Feb 03 2012
STATUS
approved