Compute the unique positive integer n such that 2⋅22+3⋅23+4⋅24+⋯+n⋅2n=2n+10.
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Let S=2⋅22+3⋅23+4⋅24+⋯+n⋅2n.Then 2S=2⋅23+3⋅24+4⋅25+⋯+n⋅2n+1.Subtracting these equations, we get S=(2⋅23+3⋅24+4⋅25+⋯+n⋅2n+1)−(2⋅22+3⋅23+4⋅24+⋯+n⋅2n)=−2⋅22−23−24−⋯−2n+n⋅2n+1=−8−23(1+2+22+⋯+2n−3)+n⋅2n+1=−8−23(2n−2−1)+n⋅2n+1=−8−2n+1+8+n⋅2n+1=(n−1)2n+1.Hence, (n−1)2n+1=2n+10, so n−1=29=512, from which n=513.