allocate mem(2^30)

base = 2
cat(x,y) = x*base^#digits(y,base)+y

a = [0]
n = 0

nb = vector(2027483)

{
	for (v=1, #nb,
		if (v<=2 || nb[v]==1,
			print (n++ " " a[n]=v);
			if (n==#a,
				a = concat(a, vector(#a));
			);

			for (i=1, n-1,
				an = cat(a[i],v);
				if (an>#nb,
						break,
						nb[an]++;
				);
			);
			for (i=1, n-1,
				na = cat(v,a[i]);
				if (na>#nb,
						break,
						nb[na]++;
				);
			);
		);
	);
}

quit