File (Field) Paths serial token
The problem is it starts from 0, isn't it?

If you use that for your path: [node:title]_a.[file:ffp-extension-original]


my_node_title_a0.jpg
my_node_title_a1.jpg
my_node_title_a2.jpg



OR

You can use the [file:original:fid] pattern, it gives serial values but the fid increments for all the nodes, not for each nodes. I mean, if you upload 10 images to your first node and then for your second node if you upload 3 images, second node's images' names are as below:


my_node_title_a11.jpg
my_node_title_a12.jpg
my_node_title_a13.jpg