first(n) = {gen = List(); seeds = List([2]); 
	res = vector(n + 1, i, oo); 
	process(2, 0); 
	for(i = 0, oo, 
		seeds = getseeds(i); 
		\\print(seeds); 
		if(#seeds == 0,
			
			return(res[^1])
		, 
			for(j = 1, #seeds, 
				process(seeds[j], i+1); 
			); 
		);
	);
		
}



children(n, ulim) = {my(c = List()); 
for(i = 1, min(n, ulim\n)-1, 
	if(res[n*(i+1)]==oo, 
		listput(c, n*(i+1))
	)
); c
}

process(n, val) = {my(i, c);
	res[n] = min(val, res[n]); 
	c = children(n, #res); 
	for(i = 1, #c, 
		process(c[i], val); 
	)
	
}

getseeds(n) = {
	my(seeds = List()); 
	for(i = 1, #res-1, 
		if(res[i] == n, 
			if(res[i-1] == oo, 
				listput(seeds, i-1); 
			); 
			if(res[i+1] == oo, 
				listput(seeds, i+1); 
			);
		)
	); listsort(seeds, 1); if(#seeds > 0 && seeds[1] == 1, listpop(seeds, 1)); seeds
}