OFFSET
1,1
COMMENTS
Conjecture: No term is zero.
Next term a(22) is too large (121 digits) to include in sequence. - Ray Chandler, Sep 23 2003
From Farideh Firoozbakht, Jan 07 2015: (Start)
The conjecture is not true. There exist many numbers n such that a(n)=0.
By using the theorem and its corollary mentioned in the comments lines of the sequence A086766, we can prove that for m = 2, 3, ..., 275 a(10^m)=0.
What is the smallest odd prime p, such that (10^(p^2)-1)/(10^p-1) is a prime number (a(10^(p-1)) is nonzero)?
What is the smallest integer m, such that m > 1 and a(10^m) is nonzero?
Conjecture: If n is not of the form 10^m then a(n) is nonzero.
(End)
EXAMPLE
a(2) = 2221 is a prime but 21 and 221 are composite.
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Sep 10 2003
STATUS
approved