A062679: Something's wrong

[Don Reble]

> Or how about the sequence "Numbers n which are not prime which have
> the digit 9 in its divisors except 1. 1691 is the first such entry.

The sequence is infinite, since there are infinitely many 100k+19 primes,
that many 100k+89 primes, and one of each multiplies to 100k+91.

The sequence might also contain all powers of 509 (except 1 and 509).
But will we ever know, whether all those powers have a nine-digit?

The problem might be tractable, if only each power had a nine in the
last N digits (for some particular N). The powers modulo 10^N are
periodic, and that could yield a proof.

Alas, the rightmost nine keeps moving left:
509^2 ends with 3 non-nine digits;
    4           5
    6          13
   16          14
  ...
12398          97
57584         129

-- 
Don Reble  djr at nk.ca