Takuya's parents gave him \$100$100dollar sign, 100 as a birthday gift. Since he loves board games, he spent \$20$20dollar sign, 20 out of his present on board games at the end of each month until his money ran out. Let f(n)f(n)f, left parenthesis, n, right parenthesis be the amount of money that remained from Takuya's present during month nnn, where n=1n=1n, equals, 1 represents the month he received his present. fff is a sequence. What kind of sequence is it?