sequences

2+3+5+10+20+..................+10240

6 Answers

i think it is 20480......

that's correct nihal..

basically S_n-S_n-1=S_n-1

t_n = 2 + (n-1)[2n²-7n + 12]6

so Sn can be easily found out now

no need of even that..

the expression i have written above is true for n>2

so we can say that S_n=2S_n-1

S_n=2^n-2S₂ = 2^n-1*5 (except if n=1)

S_n=S_n-1 + S_n-2 + S_n-3...............S₁
therefor sum is 20480
example 20=10+5+3+2 ,10=5+3+2

yes sir !!

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