A062679: Something's wrong
Don Reble
djr at nk.ca
Sat May 7 02:41:09 CEST 2005
> 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
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