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A115073
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Numbers n such that 10^(2n+1)-7*10^n-1 is prime.
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45
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1, 8, 9, 352, 530, 697, 1315, 1918, 2874, 5876, 6768
(list;
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listen;
history;
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internal format)
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OFFSET
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1,2
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REFERENCES
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C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
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LINKS
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Table of n, a(n) for n=1..11.
Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
Makoto Kamada, Prime numbers of the form 99...99299...99
Index entries for primes involving repunits.
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FORMULA
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a(n) = (A077778(n)-1)/2.
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MATHEMATICA
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Do[If[PrimeQ[10^(2n + 1) - 7*10^n - 1], Print[n]], {n, 3000}]
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PROG
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(PARI) for(n=0, 1e4, if(ispseudoprime(t=10^(2n+1)-7*10^n-1), print1(t", "))) \\ Charles R Greathouse IV, Jul 15 2011
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CROSSREFS
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Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
Sequence in context: A041142 A175849 A041605 * A042393 A114132 A038704
Adjacent sequences: A115070 A115071 A115072 * A115074 A115075 A115076
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KEYWORD
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nonn,changed
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AUTHOR
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N. J. A. Sloane, Mar 03 2006
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EXTENSIONS
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Edited by Ray Chandler, Dec 28 2010
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STATUS
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approved
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