{
	for (n=1, #a = vector(10 000),
		if (n==1,
				a[n] = 1,

				\\ mask of positions
				visited = to visit = 2^(n-1);

				while (to visit,
					p = valuation(to visit, 2);
					to visit -= 2^p;

					q = p + a[p];
					if (q < n && !bittest(visited, q),
						to visit += 2^q;
						visited += 2^q;
					);

					q = p - a[p];
					if (q > 0 && !bittest(visited, q),
						to visit += 2^q;
						visited += 2^q;
					);
				);

				a[n] = hammingweight(visited);
		);

		print (n " " a[n]);
	);
}

quit