Problem with Excel Pattern

[onetwotwelve]

Hey guys, I'm trying to fill a bunch of cells in a column with a basic formula but excel isn't recognising my pattern.
For example:
=A1
=A7
=A13

How do I make excel recognise the pattern? When I click to drag down it only moves the cell number by 1, not 6.

Any help will be greatly appreciated! Thanks!

[Teethless mama]

=index(a:a,(rows($1:1)-1)*6+1)

[onetwotwelve]

Thanks a lot! But how do I tailor the equation to have cell B5975 as the first one?