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A183181 Numbers n such that (7*10^(2n+1)-9*10^n-7)/9 is prime. 1
4, 5, 8, 11, 1244, 1685, 2009, 14657, 15118 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

LINKS

Table of n, a(n) for n=1..9.

Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)

Makoto Kamada, Prime numbers of the form 77...77677...77

Index entries for primes involving repunits.

FORMULA

a(n) = (A077788(n)-1)/2.

MATHEMATICA

Do[If[PrimeQ[(7*10^(2n + 1) - 9*10^n - 7)/9], Print[n]], {n, 3000}]

PROG

(PARI) is(n)=ispseudoprime((7*10^(2*n+1)-9*10^n-7)/9) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.

Sequence in context: A144062 A066233 A130814 * A047609 A188095 A190675

Adjacent sequences:  A183178 A183179 A183180 * A183182 A183183 A183184

KEYWORD

nonn,base

AUTHOR

Ray Chandler, Dec 28 2010

STATUS

approved

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Last modified September 23 21:15 EDT 2017. Contains 292391 sequences.