[seqfan] Re: Another chemistry related sequence?

[franktaw at netscape.net]

See http://en.wikipedia.org/wiki/Bismuth-209.  Bismuth 209 was long 
thought to be stable, but actually has a half-life of 1.9e19 years.  It 
is likely that other isotopes will be found to be slightly unstable; 
perhaps all are (proton decay is still a theoretical concept).

Frankly, I think this whole area ought to be left out of the OEIS; but 
as long as A007656 is present, I suppose there's no reason to exclude 
it.

Franklin T. Adams-Watters

-----Original Message-----
From: David Wilson <davidwwilson at comcast.net>

a(43) = 0 as well.

I think "stable" once meant "will never spontaneously decay." The 
poster boy
for stability was the proton.

Wikipedia states that protons are now thought to have minimum half-life 
of
10^36 years, yet are still called stable.

I don't find a defined half-life cutoff point where unstable becomes 
stable,
maybe it's a matter of application.


----- Original Message -----
From: "Antti Karttunen" <antti.karttunen at gmail.com>

> Here is an idea for atomic elements related sequence that should
> be reasonably well defined:
>
> a(n) = The number of stable isotopes the element number n has.
>
> If the information in Wikipedia is correct, the sequence should start 
as:
> 2,2,2,1,2,2,2,3,1,3,...
>
> Note that both a(83) ( http://en.wikipedia.org/wiki/Bismuth )
> and a(92) ( http://en.wikipedia.org/wiki/Uranium ) should be 0.
>
>
>
> (Or is it? Okay, we can speculate about the eventual decaying of 
protons,
> but... Also, I mean stable at "the normal room temperature 
conditions",
> not
> inside
> a particle accelerator.)
>
>
> Cheers,
>
> Antti.