The possible values of n are:
1, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 35, 37, 41, 43, 47
And the elements in the set are:
124,524,724,1124,1324,1724,1924,2324,2524,2924,3124,3524,3724,4124,4324,4724
So the sum of the elements in the set = 38424 = 16