popular dilutions
karttu at megabaud.fi
karttu at megabaud.fi
Thu Oct 11 11:18:33 CEST 2001
Marc wrote:
> Start with 11 (just for example) which is prime. We'll "dilute" it by
> inserting one 0 to the left of each digit, giving 0101 = 101, which is
> still prime. But if we dilute it twice by inserting two 0s we get 001001 =
> 1001, which is composite. Call n's "potency" the dilution at which n's
> primality dissolves in this way.
>
> Thus all non-primes are impotent, while 11 has potency of 2, as do 13 and
> 17. Then 19 jumps to potency 4 (since 19, 109, 1009 and 10009 are all
> prime while 100009 isn't). But the potency of 23, the next prime, is just
> 1 (since 203 is composite). And so on...
>
> The above examples present decimal potency for readability, but I'm actually
> interested in binary potency:
> 2 = 10 --> 0100 = 4 so its (binary) potency is 1
> 3 = 11 --> 0101 = 5 --> 001001 = 9 so its potency is 2
> 5 = 101 --> 010001 = 17 --> 001000001 = 65 giving 2 again
> etc
> (note that the 5 that appears as the first dilution of 3 has a different
> "successor" than undiluted 5 does).
A dumb question: Why? (it has a different successor in that case)
Yours,
Antti
>
> The binary potency of n is given by the new sequence A064891:
> 0 1 2 0 2 0 1 0 0 0 1 0 1 0 0 0 2 0 1 0 0 0 2 0 0 0 0 0 3 0 1 0 0 0 0...
>
> The binary potency of the n-th prime is now A064892:
> 1 2 2 1 1 1 2 1 2 3 1 1 1 3 3 3 1 3 1 1 1 1 2 1 1 1 1 3 1 1 1 1 1 3 4 ...
>
> The smallest value with each binary potency is A064893, to the extent that
> I have been able to compute it:
> 1 2 3 29 149 4079...
> The next term, if it exists, is a prime greater than a million.
>
> Need I say "more"? Or is sixual potency somehow taboo?
>
> Questions:
> What is the next term?
> Do all potencies appear?
> Is the sequence monotonic?
> Are there integers with infinite potency?
> What can we say about the distribution of primes in the sequence of
> dilutions of n?
>
>
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