[A006450](https://oeis.org/A006450)
by ud2_ @ 2019-07-17 14:55:14
@[sjx233](/space/show?uid=206953) 你是魔鬼吗
by Lstdo @ 2019-07-17 15:25:21
？？？
by 一块小生姜 @ 2019-07-17 21:15:34
#6 and #12 ???
by 一块小生姜 @ 2019-07-17 21:24:28