One; one
billion
, the sequence {cn} is a arithmetic progression with 1 as the first term and a tolerance of 2, and the general term formula of the sequence {cn} can be obtained;
(2) Dislocation subtraction summation.
( 1)∵anbn+ 1? an+ 1bn+2bn+ 1bn=0,cn=anbn,
∴cn? cn+ 1+2=0,
∴cn+ 1? cn=2,
∫ Two series whose first term is 1 {an}, {bn}
∴ Sequence {cn} is a arithmetic progression, the first term is 1, and the tolerance is 2.
∴cn=2n? 1;
(2)∵bn=3n? 1,cn=anbn,
∴an=(2n? 1)? 3 1? n,
∴Sn= 1×30+3×3? 1+…+(2n? 1)×3 1? n,
∴3Sn= 1×3+3×30+…+(2n? 1)×32? n,
∴? 2Sn=? 1×3? 2? (30+3? 1+…+32? n)? (2n? 1)? 3 1? n,
∴Sn=(n? 1)3 1? n+3。