How many subsets of (1; 2; 3; ... 14) have 15 as the sum of their largest and smallest elements in the subset?

(In reply to

solution (spoiler) by Charlie)

Beautiful!

Still, staying decimal , one can see it as a gometric sequence <br>

with a(o)=4 and q=4 so the sum is (surprise,surprise ):<br>

__(4^7 - 1) / (4-1)= 5461__

__isomorphic solution__

*Edited on ***May 16, 2010, 2:43 pm**