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A183183 Numbers n such that (7*10^(2n+1)+18*10^n-7)/9 is prime. 2
1, 2, 8, 19, 20, 212, 280, 887, 1021, 5515, 8116, 11852 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(13) > 10^5. - Robert Price, Jan 19 2016

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..12.

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

Makoto Kamada, Prime numbers of the form 77...77977...77

Index entries for primes involving repunits.

FORMULA

a(n) = (A077796(n)-1)/2.

MATHEMATICA

Do[If[PrimeQ[(7*10^(2n + 1) + 18*10^n - 7)/9], Print[n]], {n, 3000}]

PROG

(PARI) is(n)=ispseudoprime((7*10^(2*n+1)+18*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: A134789 A058217 A306616 * A072675 A033711 A093012

Adjacent sequences:  A183180 A183181 A183182 * A183184 A183185 A183186

KEYWORD

nonn,more,base

AUTHOR

Ray Chandler, Dec 28 2010

STATUS

approved

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Last modified September 24 17:17 EDT 2021. Contains 347651 sequences. (Running on oeis4.)