[seqfan] Re: computability of A080075 Proth numbers
guninski at guninski.com
Mon Aug 16 16:58:14 CEST 2010
On Mon, Aug 16, 2010 at 04:12:19PM +0200, Maximilian Hasler wrote:
> > a(n+1) = (-a(n - 1) + 2*a(n))
> > OR
> > a(n+1) = (-2*a(n - 1) + 3*a(n))
looks like the first branch of the OR is TRUE unless n=2^k (else the
second branch is correct).
assuming the formulas are correct this bugs me:
unless n=2^k proth numbers satisfy a linear recurrences, yet the
doubling formulas are linear.
> I considered the sequence
> b = min( -a[i-1]+2*a[i], -2*a[i-1]+3*a[i] )
this usage of |min| reminds me of "tropical semiring" where
x "+" y <-> min(x,y)
x "*" y <-> x + y
couldn't find any interesting "tropical" stuff, though...
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