rem = List([1])			\\ free values
w = 1					\\ chunk length
unseen = rem[#rem]+1	\\ values >= unseen are all free
nth(n) = {
	if (n > #rem,
		rem = List(concat(Vec(rem), [unseen..(unseen+=2*w=max(w,n))-1]));
	);
	my (v=rem[n]);
	listpop(rem, n);
	return (v);
}

{
	a = vector(10 000);
	u = 1;
	h = 1;
	for (n=1, oo,
		v = nth(h);
		if (v<=#a,
			a[v] = n;
			while (a[u],
				print (u " " a[u]);
				if (u++==#a,
					break (2);
				);
			);
		);
		h = hammingweight(v);
	);
}

quit