[seqfan] Atomic number of n-th element in the "neptunium series"

[Felix Fröhlich]

Dear SeqFans,

here is an idea for a sequence related to radioactive decay of a chemical
element:

Atomic number of n-th element in the "neptunium series", the decay chain of
neptunium-237, or 0 if the n-th link of the chain consists of more than one
element. For an overview, please see
https://en.wikipedia.org/wiki/Decay_chain#Neptunium_series

The sequence starts 93, 91, 92, 90, 88, 89, 87, 85, 83, 0, 82, 83, 81

a(10) (if the offset is 1) is 0, because bismuth-213 decays into
polonium-213 and thallium-209, both of which in turn decay into lead-209.

I don't know if this sequence is interesting. The "0" term may be a bit
unsatisfactory, but I am not sure of a better way to resolve the issue of
an isotope decaying into two daughter isotopes at the moment.

Best regards
Felix Fröhlich