[r-t] Extents of doubles

[Alexander Holroyd]

How many 24-changes/lead doubles principles are there with only two single 
changes in the lead and with no more than 2 consecutive blows?  (No rung 
ones, it seems).

On Fri, 4 Aug 2006, Philip Earis wrote:

> There are other interesting methods on the same webpage, from the familiar
> Orpheus, to Mermaid (1.3.1.3.1.5.1.3.1.3.1.125.3.5.3.5.3.1.3.5.3.5.3.145),
> which has some beautiful symmetry.
>