## Friday, 6 May 2011

### Break Building

I spent most of the Easter and May holiday week-ends watching the snooker world championship from Sheffield, in the hope that newcomer Judd Trump might win over the old guard John Higgins, and he came quite close.

Rather than abolish the May Day holiday break, surely it is time to fix the date of Easter closer to the Spring equinox, in March, so that the two holidays don't come so close. It's getting like Christmas and the New Year.

Much of the rest of my time was spent revising and checking the section on King tours on the Knight's Tour Notes pages, particularly the enumeration of the tours on boards of two ranks. The totals are given by recursion relations and by formulae involving the Fibonacci numbers. This proved quite troublesome, but maybe that's because my brain isn't working a smoothly as it did even a few years ago.

On the 2x8 board there are 128 closed tours, which is easy to verify, but the number of open tour diagrams works out to the surprisingly large, and surprisingly round number T = 32000. I still wonder whether I've got this right, but the other figures seem to be consistent with this. On the same board there are 584 reentrant tours, and G = 8176 geometrically distinct open tours, of which S = 352 are symmetric. These figures are related by G = (T + 2S)/4.