How to find the sum
16+56.12+5.86.12.18+5.8.116.12.18.24+⋯.
I have tried to make this series in the form 1+nx+n(n+1)x22!+n(n+1)(n+2)x33!+⋯. But I failed to do so. Can anyone please help me
Answer
Like Calculating 1+13+1⋅33⋅6+1⋅3⋅53⋅6⋅9+1⋅3⋅5⋅73⋅6⋅9⋅12+…?,
If S=16+56.12+5.86.12.18+5.8.116.12.18.24+⋯.
2S=26+2⋅56.12+2⋅5.86.12.18+2⋅5.8.116.12.18.24+⋯
2S+1+13
=1+−231!(−36)+−23(−23−1)2!(−36)2+−23(−23−1)(−23−2)3!(−36)3+⋯
=(1−12)−2/3
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