OFFSET
1,2
COMMENTS
The sequence was computed by D. S. McNeil.
Note that the sequence A173713 reaches 9-digit numbers fairly quickly, at index 451, but out to index 12000, it still does not reach 10-digit numbers.
The sequence A173065 (strictly increasing) seems to grow fairly slowly, with occasional big jumps, which isn't really surprising, I guess. It reaches 9-digit numbers at index 8060, and then grows very slowly.
The fact that 9-digit numbers usually get the job done is due to the relative abundance of divisors of 10^9 + 1 (32 divisors).
Note that 10^15 + 1 has 128 divisors, and so it seems very unlikely to me that you could ever reasonably calculate the sequence far enough to the point where 15-digit numbers would not suffice... (End)
REFERENCES
Eric Angelini, Posting to Sequence Fans Mailing List, Sep 21 2010
LINKS
Eric Angelini, |a-b| divides concatenation [ab]
E. Angelini, |a-b| divides concatenation [ab] [Cached copy, with permission]
Jack Brennen, PARI Program
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 25 2010
STATUS
approved