Postgres generate series with exactly 100 steps

Lets say we have the dates

'2017-01-01'
and
'2017-01-15'

and I would like to get a series of exactly N timestamps in between these dates, in this case 7 dates:

SELECT * FROM 
    generate_series_n(
        '2017-01-01'::timestamp,
        '2017-01-04'::timestamp,
        7
    )

Which I would like to return something like this:

2017-01-01-00:00:00
2017-01-01-12:00:00
2017-01-02-00:00:00
2017-01-02-12:00:00
2017-01-03-00:00:00
2017-01-03-12:00:00
2017-01-04-00:00:00

How can I do this in postgres?

>Solution :

You can divide the difference between the end and the start value by the number of values you want:

SELECT * 
FROM generate_series('2017-01-01'::timestamp, 
                     '2017-01-04'::timestamp, 
                     ('2017-01-04'::timestamp - '2017-01-01'::timestamp) / 7)

This could be wrapped into a function if you want to avoid repeating the start and end value.