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A183181 Numbers k such that (7*10^(2*k+1) - 9*10^k - 7)/9 is prime. 2
4, 5, 8, 11, 1244, 1685, 2009, 14657, 15118, 20332, 50830, 75062 (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
Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
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
Sequence in context: A144062 A066233 A130814 * A310575 A047609 A360993
KEYWORD
nonn,base
AUTHOR
Ray Chandler, Dec 28 2010
EXTENSIONS
a(10) from Robert Price, Oct 07 2023
a(11) from Robert Price, Oct 17 2023
a(12) from Robert Price, Dec 06 2023
STATUS
approved

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Last modified March 29 08:59 EDT 2024. Contains 371268 sequences. (Running on oeis4.)