q^(3 + 3*n) - q^(7 + 6*n) - q^(8 + 7*n) + q^(10 + 10*n) + 
 (q^(13 + 12*n) - q^(13 + 13*n))*f[n] + (-1 + q^(2 + n))*f[2 + n]
