how to make a formula?

i have a problem where i need to find a formula where i only know x and y. i dont know if i can use x² or not or something else. so is there a way if i have this values?
1=6 (1*6)
2=18 (1*6+2*6)
3=36(1*6+2*6+3*6)

what i can see and have counted this follow that x*6+(x-1)*6+(x-2)*6 and so on unitel the parantese equals to 0. how do i figure out a formula that worx so i dont have to keep hitting it like that, if i reach big numbers like 20 (its big for this) i have to type alot

can some one lock this? there is no use for this anymore