first(n) = {n = max(n, 4);
	my(v = vector(100), res = vector(n), maxused = 4); 
	for(i = 1, 4, res[i] = i; v[i] = 1); 
	for(i = 5, n, 
		s = 0;
		
		forvec(x = vector(2, j, [i-3, i-1]),
			s+=(gcd(res[x[1]], res[x[2]]) != 1);
			
		,
		2
		);
		target = 1-s;
		proceed = 1;
		if(2*maxused > #v, 
			v = concat(v, vector(2*maxused - #v));
		);
		for(j = 1, #v, 
			if(proceed = 0, next(2));
			
			if(v[j] == 0, 
				s = 0;
				for(k = i-3, i-1, 
					s+=(gcd(j, res[k]) != 1);
				);
				if(s == target, 
					
					res[i] = j;
					v[j] = 1; 
					maxused = max(maxused, j);
					proceed = 0;
					next(2);
				)
			)
		);
		
	); res
}