Full Idea
There is surely no number n such that "n grains of sand do not make a heap, although n+1 grains of sand do" is true.
Gist of Idea
Surely there is no exact single grain that brings a heap into existence
Source
Michael Dummett (Truth and the Past [2001], 4)
Book Reference
Dummett,Michael: 'Truth and the Past (Dewey Lectures)' [Columbia 2004], p.60
A Reaction
It might be argued that there is such a number, but no human being is capable of determing it. Might God know the value of n? On the whole Dummett's view seems the most plausible.