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Concrete mathematics : a foundation for computer science

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<strong>for</strong> all m. Divide by n and let n + co; the limit is less than 011 . . . CX, <strong>for</strong><br />

all m. Finally we have<br />

011 . .a, =<br />

A ANSWERS TO EXERCISES 573<br />

1 1<br />

9.46 For convenien.ce we write just m instead of m(n). By Stirling’s approximation,<br />

the maximum value of k:/k! occurs when k z m z n/inn, so<br />

we replace k by m + k and find that<br />

ln Cm+ kin<br />

(m-t k)!<br />

In 27rm<br />

:= nlnm-mlnmfm-P<br />

2<br />

(m+n)k2<br />

2m2<br />

+ O(k3m ‘logn)<br />

Actually we want to replace k by [ml + k; this adds a further 0 (km ’ log n).<br />

The tail-exchange method with lkl < m’/2+E now allows us to sum on k,<br />

A truly Be/l-shaped giving a fairly sharp asymptotic estimate<br />

summand.<br />

b, = - -<br />

The requested <strong>for</strong>mula follows, with relative error 0 (log log n/log n).<br />

9.47 Letlog,n=l+El,whereO$8

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