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A115073
Numbers n such that 10^(2n+1)-7*10^n-1 is prime.
46
1, 8, 9, 352, 530, 697, 1315, 1918, 2874, 5876, 6768, 62938, 134739
OFFSET
1,2
REFERENCES
C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
FORMULA
a(n) = (A077778(n)-1)/2.
MATHEMATICA
Do[If[PrimeQ[10^(2n + 1) - 7*10^n - 1], Print[n]], {n, 3000}]
PROG
(PARI) for(n=0, 1e4, if(ispseudoprime(t=10^(2*n+1)-7*10^n-1), print1(t", "))) \\ Charles R Greathouse IV, Jul 15 2011
KEYWORD
nonn,base
AUTHOR
N. J. A. Sloane, Mar 03 2006
EXTENSIONS
Edited by Ray Chandler, Dec 28 2010
Added two more terms from PWP table, by Patrick De Geest, Nov 05 2014
STATUS
approved