s = 0
unseen = 1
seen(v) = bit test(s, v)
see(v) = s = bit or(s, 2^v); while (seen(unseen), unseen++)

other(pp,p,m) = {
	forstep (v=unseen + (unseen%2 != m), oo, 2,
		if (!seen(v) && gcd(v, p)==1 && gcd(v, pp)>1,
			return (v);
		);
	);
}

{
	for (n=1, 10 000,
		if (n<=3,
				v = n,
				v = other(pp, p, n%2);
		);
		see(v);
		print (n " " v);
		[pp,p]=[p,v];
	);
}

quit