Advise, please, how to get the following macros working:

Sub íÁËÒÏÓ1()
For a = 1 To 1000 Step 15
Rows("a:a").Select
Application.CutCopyMode = False
Selection.Copy
Rows("a+1:a+14").Select
ActiveSheet.Paste
Next
End Sub

Mission: to select every 15-th row, to copy and paste it to the following
15 rows.
Trouble: it doesn't accept variables as numbers of rows.
What should be syntax: Rows("a:a").Select ?