Consider the sequence an given by a1=12,an+1=a2n+an Let Sn=1a1+1+1a2+1+...........+1an+1 then find the value of [S2012], where [.] denotes greatest integer function.
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Solution
an+1=a2n+an=an(an+1) ⇒1an+1=1an(an)+1=1an−1an+1 ⇒1an+1=1an−1an+1⇒1an+1=1an−1an+1 Now S2012=1a1+1+1a2+1+1a3+1+....+1a2012+1 =(1a1−1a2)+(1a2−1a3)+.......+(1a2012−1a2013) S2012=1a1−1a2013....(i) Again a1=12 ⇒a2=12+14=34,a3=34+916>1