Show the route from Philadelphia to Erie
passing once through all the towns.
 

The map shows twenty-three prominent cities of Pennsylvania
connected by bicycle routs of more or less artistic design.
The problem is a simple one: start on your summer outing
and go from Philadelphia to Erie, passing once through every
one of the cities and without going over any road twice.
That is all there is to it.

The cities are numbered to enable solvers to describe their
routes by a sequence of figures.  In this trip the usual
practice of getting there by the "shortest route possible"
will be dispensed with.  Just get there, without minding
the cyclometer.
 
 
 
 
 
 

¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»§«¤
 

                 THE SOLUTION
 

The only possible route by which all towns can be visited
but once is to take them in the following sequence:
Philadelphia to 15, 22, 18, 14, 3, 8, 4, 10, 19, 16, 11,
5, 9, 2, 7, 13, 17, 21, 20, 6, 12, and then to Erie.