q 21 − 2 q 19 + q 17 − 2 q 15 + q 11 + 3 q 7 − q 5 + q 3 {\displaystyle q^{21}-2q^{19}+q^{17}-2q^{15}+q^{11}+3q^{7}-q^{5}+q^{3}}
