A103314 conjecture
Mitchell Harris
harris at tcs.inf.tu-dresden.de
Thu May 19 21:50:02 CEST 2005
On Thu, 19 May 2005, David Wilson wrote:
>T. D. Noe wrote:
>
>> a(3^n) = 2^(3^(n - 1))
>> a(5^n) = 2^(5^(n - 1))
>> a(6^n) = a(6)^(6^(n - 1)) = 10^(6^(n - 1))
>
>(where a(n) = A103314(n)).
>
>These would all follow from my conjecture that
>
> [1] a(n) = a(s(n))^(n/s(n))
>
>where s(n) = A007947(n) is the squarefree kernel of n (product of primes
>dividing n).
>
>Now s(p^k) = p (k >= 1), so applying [1] gives
>
> a(p^k) = a(p)^(p^(k-1)) (k >= 1)
>
>But a(p) = 2 for prime p (have we proved this?), and so
>
> a(p^k) = 2^p^(k-1).
>
>Special cases p = 3 and p = 5 give your first two observations.
>
>Similarly, s(6) = 6, and so [1] gives
>
> a(6^k) = a(6)^6^(k-1)
>
>as you observed. But a(pq) = 2^p+2^q-2, so a(6) = 10, giving
>
> a(6^k) = 10^6^(k-1).
What I have so far (corroborating this) is:
if p is prime,
f(p) = 2 (obvious, either all or none)
f(p^n) = 2^(p^(n-1)) (there are n copies of a p-star, one vector of the
star defines the rest so there are p^(n-1) choices, take any subset of those)
if p and q are both prime,
then f(pq) = 2^p + 2^q - 2 (all subsets of either p or of q, but
that over counts the 2 of all or none)
and f(p^n q^m) = f(pq)^{p^{n-1} q^{m-1}} (this is conjectured (it fits
the numbers! ) but looks "right" given the resoning above and
corresponds to the more general conjecture).
The difficulty is with numbers having more than two prime factors
because of the possibility of interaction. The smallest such n is
30=2*3*5. a 5-star and 3-star can be combined to make an "off" 6-star
(Wouter's example). The "base case" of square free numbers needs
to be worked out.
What was the reasoning behind a(30) = 146854?
--
Mitch
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