OFFSET
1,1
COMMENTS
Prime versus probable prime status and proofs are given in the author's table.
a(13) > 2*10^5. - Robert Price, Jan 19 2016
REFERENCES
C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
LINKS
Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)
Makoto Kamada, Prime numbers of the form 77...77977...77
FORMULA
a(n) = 2*A183183(n) + 1.
EXAMPLE
17 is a term because 7*(10^17 - 1)/9 + 2*10^8 = 77777777977777777.
MATHEMATICA
Do[ If[ PrimeQ[(7*10^n + 18*10^Floor[n/2] - 7)/9], Print[n]], {n, 3, 23800, 2}] (* Robert G. Wilson v, Dec 16 2005 *)
CROSSREFS
KEYWORD
more,nonn,base
AUTHOR
Patrick De Geest, Nov 16 2002
EXTENSIONS
Name corrected by Jon E. Schoenfield, Oct 31 2018
STATUS
approved