The general term for this sequence is ...
[tex]3 - 5n[/tex]
If n = 1, then
[tex]3 - 5(1) \\ 3 - 5 \\ - 2[/tex]
if n = 2, then
[tex]3 - 5(2) \\ 3 - 10 \\ - 7[/tex]
if n = 3, then
[tex]3 - 5(3) \\ 3 - 15 \\ - 12[/tex]
Actually this is an "Arithmetic Sequence" but since you're asking a general term for this, 3 -5n also applies