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A093945
Primes of the form 5*10^n - 1.
3
499, 4999, 49999, 4999999, 499999999999999, 4999999999999999999999999999999999999999999999999999999
OFFSET
1,1
COMMENTS
Equivalently, primes of the form 4*10^n + 9*R_n, where R_n is the repunit (A002275) of length n.
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
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
The next term -- a(7) -- has 211 digits. - Harvey P. Dale, Feb 20 2016
MATHEMATICA
Select[Table[FromDigits[PadRight[{4}, n, 9]], {n, 60}], PrimeQ] (* Harvey P. Dale, Feb 20 2016 *)
CROSSREFS
Cf. A056712 (corresponding n).
Cf. A067206.
Sequence in context: A178044 A230004 A203735 * A184146 A214191 A132475
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Apr 17 2004
STATUS
approved