Question Number 94661 by msup by abdo last updated on 20/May/20
$${calculate}\:\Sigma\:{a}_{{n}} {x}^{{n}} \:{if}\:{a}_{{n}} \:{verify} \\ $$$${a}_{{n}+\mathrm{1}} ={a}_{{n}} \:+{a}_{{n}−\mathrm{1}} \\ $$
calculate-a-n-x-n-if-a-n-verify-a-n-1-a-n-a-n-1-