S1=a1=1
a(n+1)=S(n+1)-Sn=Sn(n+2)/n
S(n+1)=2Sn(n+1)/n
S2=2S1 *2/1
S3=2S2 *3/2
...
Sn=2S(n-1)*n/(n-1)
以上各式相乘得:Sn=2^(n-1)S1*n=n*2^(n-1)
因此Sn单调递增.
S9=9*2^8=2304>2007
因此只要取N0>=9的任一自然数即可.
S1=a1=1
a(n+1)=S(n+1)-Sn=Sn(n+2)/n
S(n+1)=2Sn(n+1)/n
S2=2S1 *2/1
S3=2S2 *3/2
...
Sn=2S(n-1)*n/(n-1)
以上各式相乘得:Sn=2^(n-1)S1*n=n*2^(n-1)
因此Sn单调递增.
S9=9*2^8=2304>2007
因此只要取N0>=9的任一自然数即可.