big = 20 000
s = 0
S = Set([])
unseen = 1
seen(v) = if (v < big, bit test(s, v), set search(S, v))
see(v) = if (v < big, s = bit or(s, 2^v), S = set union(S, Set([v]))); while (seen(unseen), unseen++)

\\ we keep only track of small values
small = []

{
	for (x=0, 1000,
		if (x>1,
			\\ find multiple of previous small values
			my (extra=[]);
			forstep (s=#small, 1, -1,
				forstep (m=ceil(unseen/small[s])*small[s], big, small[s],
					if (!seen(m),
						see(m);
						extra = concat(extra, m);
						break;
					);
				);
			);
			small = concat(small,extra);
		);
		print (x " " unseen);
		small = concat(small, unseen);
		see(unseen);
		if (unseen>=big,
			break;
		);
	);
}

quit