如图
a(n+1)
=2an , n is odd
=an +1 , n is even
ie
a1=1
n=1, a2= a1+1 =1+1=2
a(2n-1) = a(2n-2) +1
= 2a(2n-3) +1
a(2n-1) +1 = 2[ a(2n-3) + 1]
=> { a(2n-1) + 1 } 是等比数列， 公比=2
a(2n-1) + 1 = 2^(n-1) . ( a1 +1)
=2^n
a(2n-1) = -1+ 2^n
//
a(2n) = 2a(2n-1)
=2[ a(2n-2) + 1]
a(2n) + 2 =2[ a(2n-2) + 2]
=> { a(2n) + 2 } 是等比数列， 公比=2
a(2n) + 2 = 2^(n-1) .(a2 + 2)
=2^(n+1)
a(2n) =-2 + 2^(n+1)
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