[math-fun] Iterated square root puzzle

Find a closed form for the the expression sqrt(1/2^(2^0) + sqrt(1/2^(2^1) + sqrt(1/2^(2^2) + ...))). --Dan P.S. No fair using electronic assistance. _____________________________________________________________________ "It don't mean a thing if it ain't got that certain je ne sais quoi." --Peter Schickele