How to enter an array of non-adjacent cells as first argument in trend function?

Question

I want to find the value for A3.

__|_A___
1 | 5
2 | 10
3 | blank
4 | 20

So in A3 I add this:

=trend( {A1,A2,A4}  ,  {1,2,4}  ,  {3}  )

That produces an error.

Answer 1

Using INDEX:

=TREND(INDEX(A:A,{1,2,4}),{1,2,4},{3})