codeforces 569 D. Symmetric and Transitive (组合数学　第二类斯特林数　贝尔数)

Fri, 14 Aug 2015 22:20:00 +0000

D. Symmetric and Transitive

time limit per test

1.5 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Little Johnny has recently learned about set theory. Now he is studying binary relations. You’ve probably heard the term “equivalence relation”. These relations are very important in many areas of mathematics. For example, the equality of the two numbers is an equivalence relation.

贝尔数(集合的划分数目)

Fri, 14 Aug 2015 21:53:00 +0000

http://baike.baidu.com/link?url=kw5Kxe3nSvRJR0TpJUpMrORcQL8fyZFpJlT9_o0RlGYOy0bKFobabPPSj3LxGfy7o1qGVycrYK4Iags3hMFq0a

在组合数合里，贝尔数给出了集合划分的数目，以数学家埃里克·坦普尔·贝尔（Eric Temple Bell）命名，是组合数学中的一组整数数列。[1]

以B0= B1=1为始，首几项的贝尔数为：1, 1, 2, 5, 15, 52, 203, 877, 4140, 21147, 115975, …（OEIS的A000110数列）

贝尔数 on 111qqz's blog

codeforces 569 D. Symmetric and Transitive (组合数学 第二类斯特林数 贝尔数)

贝尔数(集合的划分数目)

codeforces 569 D. Symmetric and Transitive (组合数学　第二类斯特林数　贝尔数)