(4,7,12,19) how do you right this in recursive and explicit pls

You can see how the difference between two consecutive terms is constantly increasing:

So, for the next terms we'll have to add +9, +11, +13 and so on.

Also, note that is obtained by adding the 2nd odd number to , is obtained by adding the 3rd odd number to , and so on.

So, the recursive formula is

For the explicit formula, recall that the sum of the first n odd numbers is n squared. Taking into account the fact that we're not starting from 1, we have

i pretty sure it is