Question Number 134839 by SOMEDAVONG last updated on 07/Mar/21
$$\mathrm{Solve}\:,\:\mathrm{S}_{\mathrm{n}} =\:\mathrm{1}+\mathrm{2}×\mathrm{2}+\mathrm{3}×\mathrm{2}^{\mathrm{2}} +\mathrm{4}×\mathrm{2}^{\mathrm{3}} +...+\mathrm{n}×\mathrm{2}^{\mathrm{n}−\mathrm{1}} . \\ $$
Commented by mr W last updated on 07/Mar/21
$${see}\:{Q}\mathrm{134200} \\ $$