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A093945 Primes of the form 5*10^n - 1. 3
499, 4999, 49999, 4999999, 499999999999999, 4999999999999999999999999999999999999999999999999999999 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..6.

Makoto Kamada, Prime numbers of the form 499...99.

Index entries for primes involving repunits.

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

Adjacent sequences:  A093942 A093943 A093944 * A093946 A093947 A093948

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Apr 17 2004

STATUS

approved

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Last modified December 18 18:39 EST 2018. Contains 318243 sequences. (Running on oeis4.)