A pretty picture for Christmas ...

[Ralf Stephan]

> It's not hard to prove that the d(i) wind around the origin arbitrarily often 
> (i.e.,putting a(i) = arg(d(i)/d(i-1)), the sum of the angles a(i) diverges). 
> So one integer sequence you get is the sequence of i-s where the d(i) cross 
> the positive real axis. This begins as follows:
> 
>     1   17    54   110   186   281   396   532   686   861

You didn't say that's (probably) A072895 (maybe because you searched 
for 1,17,54?). The formula looks good, however.


ralf
P.S. Always delete leading one-digit numbers when searching and the
sequence grows like this.