利用对数的换底公式得:an=log(n+1) (n+2)=log2 (n+2)/log2 (n+1)
a1•a2•a3•……ak
= [log2 3/log2 2]•[log2 4/log2 3] [log2 5/log2 4]•……log2 (n+2)/log2 (n+1)
=log2 (n+2)/ /log2 2
=log2(n+2)
n+2必须是2的n次幂,a1a2...ak才可以取到整数
企盼数的和=（4-2）+（8-2）+（16-2）+…………+（1024-2）
=2^2+2^3+…………+2^10-2*9
=2026.