  We prove divisibility results for the Fourier coefficients of canonical basis
elements for the spaces of weakly holomorphic modular forms of weight $0$ and
levels $6, 10, 12, 18$ with poles only at the cusp at infinity. In addition, we
show that these Fourier coefficients satisfy Zagier duality in all weights, and
give a general formula for the generating functions of such canonical bases for
all genus zero levels.
