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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 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..13. 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. 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 CROSSREFS Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187. Sequence in context: A294468 A041605 A239524 * A298020 A042393 A264777 Adjacent sequences: A115070 A115071 A115072 * A115074 A115075 A115076 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

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Last modified February 27 08:19 EST 2024. Contains 370367 sequences. (Running on oeis4.)