Format the series_index, uses the finish_formatting command to duplicate the effects of {field:0>3s|prefix|suffix}
Code:
program:
prefix_if_series = strcat(
field('series'),
' - (',
field('publisher'),
')/[',
finish_formatting(
field('series_index'),
'0>3s', '', ''
),
'] - '
);
final = strcat(
test(
field('series'),
prefix_if_series,
''
),
field('title'),
' - ',
field('authors')
);