In CaCO3, we have 1 Ca atom, 1 C atom, and 3 O atoms. So in 4CaCO3, we have 4 * 1 = 4 Ca atoms, 4 * 1 = 4 C atoms, and 4 * 3 = 12 O atoms.

Therefore, the total number of atoms in 4CaCO3 is 4 + 4 + 12 = 20 atoms.