Drag a formula, so that it increases by 17 each time
This formula will return A17. When draged down it will return the values in A34, A51, A68, etc. i.e. every 17th row.
=INDEX(A:A,(ROW()*17))
If you want to start in a different row, say row 10, you need to subtract the respective number from the starting row, like 7.
=INDEX(A:A,(ROW()*17)-7)