The best I have found is a sum of 1095:
{5,6,7,8,9,19,28,28,37,38,39,46,47,48,49,56,57,58,59,67,68,69,78,79,89}
Incidentally the name of this puzzle comes from the Carol The Twelve Days of Christmas which features sets of 12, 11, etc.
http://www.stetson.edu/~efriedma/mathmagic/0802.html is another type of puzzle using this idea. |