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Concrete mathematics : a foundation for computer science

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A ANSWERS TO EXERCISES 503<br />

4.32 The q(m) nu:mbers { kn mod m 1 k I m and 0 < k < m} are the numbers<br />

{k 1 k I m and 0 6 k < m} in some order. Multiply them together and<br />

divide by nOskcm, klm k.<br />

4.33 Obviously h(1) = 1. If m I n then h(mn) = td,mn f(d) g(mn/d) =<br />

tc\m,*\n f(cd) g((m./c)(n/d)) = Xc,, Ed,,, f(c) s(m/cl f(d) g(nld); this is<br />

h(m) h(n), since c 1. d <strong>for</strong> every term in the sum.<br />

4.34 g(m) = x:d,mf(d) = x.d,mf(m/d) = Eda, f(m/d) if f(x) is zero<br />

when x is not an integer.<br />

4.35 The base cases are<br />

I(O,n) = 0; I(m,O) = 1.<br />

When m,n > 0, there are two rules, where the first is trivial if m > n and<br />

the second is trivial if m < n:<br />

I(m,n) = I(,m,nmodm) - [n/mJI(nmodm,m);<br />

I(m,n) = I(,m mod n,n) ,<br />

4.36 A factorization of any of the given quantities into nonunits must have<br />

m2 - 10nZ = f2 or :&3, but this is impossible mod 10.<br />

4.37 Let a, = 2-“ln(e, - 5) and b, := 2-“ln(e, + i). Then<br />

en=[E2”+iJ w a,$lnE

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