1, divisible by an;
2. Except the ending term without a, such as constant, (2 n- 1), etc.
3. Except an.a(n+ 1)
This problem is the same as dividing an.a(n+ 1).
Get1/(a (n+1))-1/an = 2,
{1/an} is the arithmetic progression whose first term is 1/a 1= 1 with a tolerance of 2.
1/an = 1+2(n- 1)= 2n- 1
an= 1/(2n- 1)。
After testing, a 1 is also suitable.
After this problem is solved, bn is easy to find and can be obtained in a generation.
bn=2^(n-2)
(2)cn= 1/[n-2+2]= 1/n
1/(cn)^2= 1/n^2< 1/[(n- 1)n]= 1/(n- 1)- 1/n
Tn= 1+ 1/2^2+...+ 1/n^2< 1+[ 1- 1/2+ 1/2- 1/3+...+ 1/(n- 1)- 1/n]
=2- 1/n
The Chinese textbook for primary schools in Changsha adopts the unified edition published by People's Education Press, while the