I'm not an expert on this, but the sequence looks like either 766, 765, or 7675. I believe you read these types from the top, to bottom left, and then across.
I'm leaning towards the second and third options, as there is a clear break on the right side of the bottom line. Also, do you have a picture showing the top of the triangle above the "7"? That may indicate a fifth number in the sequence; such as "66775".