a(n+1)=(1+1/n)an+(n+1)/2^n
bn=an/n,an=nbn
(n+1)b(n+1)=(1+1/n)nbn+(n+1)/2^n
b(n+1)=bn+1/2^n=bn+（1/2)^n
bn=b(n-1)+)(1/2)^(n-1)
.
bz=b1+(1/2)^1
相加的：bn=b1+(1/2)^(1)+.+(1/2)^(n-1),b1=a1/1=1
bn=1+(1/2)^(1)+.+(1/2)^(n-1)=(1/2)^0+(1/2)^(1)+.+(1/2)^(n-1)
bn=(1-(1/2)^n)/(1-1/2)=2(1-(1/2)^n)=2(1-1/(2)^n)=2-1/2^(n-1)
an=2n-n/2^(n-1),