q 13 − 4 q 12 + 8 q 11 − 13 q 10 + 18 q 9 − 21 q 8 + 21 q 7 − 19 q 6 + 15 q 5 − 10 q 4 + 6 q 3 − 2 q 2 + q {\displaystyle q^{13}-4q^{12}+8q^{11}-13q^{10}+18q^{9}-21q^{8}+21q^{7}-19q^{6}+15q^{5}-10q^{4}+6q^{3}-2q^{2}+q}
