login
A183187
Numbers k such that 10^(2k+1)-10^k-1 is prime.
47
26, 378, 1246, 1798, 2917, 23034, 47509, 52140, 67404
OFFSET
1,1
COMMENTS
944264 is a term but its position is not known. - Jeppe Stig Nielsen, Jan 12 2024
a(10) > 300000. - Serge Batalov, Jan 17 2024
REFERENCES
C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
FORMULA
a(n) = (A077794(n)-1)/2.
MATHEMATICA
Do[If[PrimeQ[10^(2n + 1) - 10^n - 1], Print[n]], {n, 3000}]
PROG
(PARI) for(n=1, 1e3, if(ispseudoprime(10^(2*n+1)-10^n-1), print1(n", "))) \\ Charles R Greathouse IV, Jul 15 2011
KEYWORD
nonn,more,base
AUTHOR
Ray Chandler, Dec 28 2010
STATUS
approved