9. n is a non-negative integer, express (1+432−434) as (1+432−434) " =aa+ba32+ca34, where an,bn,ca are integers. Prove: if cn=0, then n=0.
Solution
9. Given (1+432−434)n+1=(a0+b032+c034)(1+432−434)
we get an+1=a0−8bn+8cn
Since a0=1, all a0 are odd. Every non-zero integer k can be expressed as k=2p⋅k′, where k′ is odd and p⩾0. Define v(k)=p. Let β0=v(bn),γ0=v(c0). (1) For non-negative integer t,β2t=γ2t=t+2. Prove: When t=0, b1=4,c1=−4.
The above assertion holds. Assume β2t=γ2t=t+2, then since ==(a+2t+2(b32+c34))2a2+2t+3a(b32+c34)+22t+4(b32+c34)2A+2t+3(B32+C34).
When a,b,c are odd, A,B,C are odd, thus β2t+1=γ2t+1=t+3, hence the assertion holds for all non-negative integers. (2) If n,m are integers, bn,cn,bm,cm are non-zero, βn=γ0=λ,βm=γm=μ,μ<λ, then bn+m,cn+m are non-zero, and βn+m=γn+m=μ. Prove: By (a′+2λ(b′32+c′34)) (a′′+2μ(b′′32+c′′34))=A+2μ(B32+C34),
When a′,a′′;b′,b′′,c′,c′′ are odd, A, B,C are all odd. (3) For every integer n⩾1, let n=2tr+2tr−1+⋯+2t1,0⩽t1<⋯<tr,
then cn is non-zero, and γn=t1+2. Proof: This follows from (1) and (2). From (3), the conclusion of the problem is established. Note: b1080 and c1980 are divisible by 4 but not by 8.
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