Yeah, it's 17,179,869,184 tiles for the entire earth 4^(N-1), where N is number of zoom levels, which is 18. Granted, a great deal of these redirect to their solid blue ocean tile.
How did you come up with that number? The sum loop that follows reports 524287 tiles total.
#include <stdio.h> #include <math.h> int main(void) { int i; double tot = 0; for(i = 0; i <= 18; ++i) tot += exp2(i); printf("tot %f\n", tot); return 0; }