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设Bn=3/(AnAn+1),An=6n%5,tn是数列{Bn}的前n项和...

Tn =b1+b2+...+bn =(3/a1a2)+......+3/[ana(n+1)] =3[1/a1a2+1/a2a3+...+1/ana(n+1)] =3[1/(1*7)+1/(7*13)+...+1/(6n-5)(6n+1)] =3{(1/6)(1-1/7)+(1/6)(1/7-1/13)+...+(1/6)[(1/6n-5)-1/(6n+1)]} =(1/2)*[1-1/7+1/7-1/13+........+1/(6n-5)+1/(6...

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