Your basically adding the first 3 numbers to get the next for example: 1,1,1=3
and then 1,1,3,=5 and then 1,3,5=9 then 3,5,9 =17 so on and so forth.
so to get the first answer of 105 I added the last 3 numbers in the sequence together (17,31,57) to get 105
the next 3 numbers in the sequence are:
105,193,355