Postgres settings reported differently in pgsql
I see the same difference on my test database:

show shared_buffers;
 shared_buffers 
────────────────
 768MB


select name, setting from pg_settings where name = 'shared_buffers';
      name      │ setting 
────────────────┼─────────
 shared_buffers │ 98304


Then watching the numbers for a short while, I set up the following query:

SELECT 98304 * 8192 / (1024 * 1024);
 ?column? 
──────────
      768


So, to me it looks like that pg_settings reports these sizes in 8 kb pages (8192 refers to this fact).

Note that there is a third way to check settings, namely the current_setting() function:

SELECT current_setting('shared_buffer');
 current_setting
-----------------
 768MB