Look at the differences:
590 1150 4940 6480 8120
......560...3790.1540.1640
The numbers should increase as the p+:e- ratio increases, but 3790 is a big jump, i.e. MUCH more energy than might be expected is needed. This is caused by the e- is being removed from a new shell.
Put another way, the first e- is fairly easy to remove, the second one is about twice as hard, the third one is much harder, the fourth is a bit harder etc.
BTW, it is Ca.