Beautiful from collections import defaultdict d = defaultdict(list) for i in range(2, 10000): for y in d.pop(i, [i]): d[i + y].append(y)

Beautiful from collections import defaultdict d = defaultdict(list) for i in range(2, 10000): for y in d.pop(i, [i]): d[i + y].append(y) for y in sorted(y for x in d.values() for y in x): print(y)