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A115073 Numbers n such that 10^(2n+1)-7*10^n-1 is prime. 45
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: A175849 A041605 A239524 * A042393 A264777 A114132

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 September 23 21:16 EDT 2017. Contains 292391 sequences.