We see on the picture that :
When we go down one row, we add one horizontal and two diagonal cards.
In the first row we have 2 cards
In the second 2+3=5 cards
In the third 5+3=8 cards
etc.
General formula : in the n-th row from the top, we have[tex]\boxed{ 2+(n-1)\cdot3\text{ cards}}[/tex]
