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Mathematics版 - a small question
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1 (共1页)
w***d
发帖数: 17
1
let f(n,r) be the number of ways to arrange the numbers 1,2, ..., n in a line
so that exactly r numbers match their correct positions. For example, if n =5,
then 1 4 3 5 2 has 2 matches: 1 is in the 1st position, and 3 is in the 3rd
positions; 1 2 3 4 5 has 5 matches.
Then is there an explicit expression for f(n,r)? Thx a lot!!!
w***d
发帖数: 17
2
哪位大侠帮个忙啊,着急要阿

line
5,

【在 w***d 的大作中提到】
: let f(n,r) be the number of ways to arrange the numbers 1,2, ..., n in a line
: so that exactly r numbers match their correct positions. For example, if n =5,
: then 1 4 3 5 2 has 2 matches: 1 is in the 1st position, and 3 is in the 3rd
: positions; 1 2 3 4 5 has 5 matches.
: Then is there an explicit expression for f(n,r)? Thx a lot!!!

1 (共1页)
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来一道题方程解答
Help:请问如何用matlab或者其他软件计算exp(1/t-t)的积分呀?请教一个LaTex参考文献问题
A hyperbola question求助数论专家-psi(x)的“explicit formula".
Help a problem about three-dimension convolutionRe: latex问题(integral)
相关话题的讨论汇总
话题: matches话题: positions话题: numbers话题: question话题: small