You will need a periodic table to help you answer this problem. The atomic numbers are arrange from lowest to highest in the periodic table. You can locate element number 55 to be Cesium with an atomic weight of 132.905 amu. So, you start from element 56. The following elements are:
56 Barium 137.328 amu
57 Lanthanium 138.905 amu
58 Cerium 140.116 amu
59 Praseodymium 140.908 amu
60 Neodymium 144.243 amu
Neodymium is already greater than 144 amu. Therefore, these elements only include Barium, Lanthanium, Cerium and Praseodymium.
