explicit formula of 4 10 18 28

Question

explicit formula of 4 10 18 28

Answer 1

YOU NEED TO PRACTICE PUTTING A QUESTION INTO ENGLISH!

 

It appears to me that, to advance from a number to get to the next, one adds 6 in the first instance, then 8 in the second instance, and then 10 in the third instance.

 

See if this works.  a₁ = 4   a_i = a_i-1 + 2(i+1) for i = 2 & up.