SQL> with t
  2  as
  3  (
  4  select 'Blank:1,3,17' str from dual
  5  )
  6  select regexp_substr(str, '.*:') ||regexp_substr(str,'[url=/wiki/:digit:]:digit:[/url]+',1,LEVEL) str
  7    from t
  8  connect by level <= length(regexp_replace(str,'[^,]'))+1
  9  /

STR
------------------
Blank:1
Blank:3
Blank:17

SQL> var str varchar2(50)
SQL> exec :str := 'Blank:1,3,17'

PL/SQL procedure successfully completed.

SQL> with 
  2    lines as (select level line from dual connect by level <= 3),
  3    data as (
  4     select substr(:str,1,instr(:str,':')) prefix,
  5            ','||substr(:str,instr(:str,':')+1)||',' value
  6     from dual
  7    )
  8  select prefix||' '||
  9         substr(value, instr(value,',',1,line)+1,
 10                       instr(value,',',1,line+1)-instr(value,',',1,line)-1)
 11           value
 12  from data, lines
 13  /
VALUE
--------------------------------------
Blank: 1
Blank: 3
Blank: 17

3 rows selected.

SQL> create or replace procedure p (str in varchar2, cur out sys_refcursor) 
  2  as
  3  begin
  4    open cur for
  5      'with 
  6         input as ( select :str str from dual ),
  7         lines as ( select level line from dual connect by level <= 3 ),
  8         data as (
  9           select substr(str,1,instr(str,'':'')) prefix,
 10                  '',''||substr(str,instr(str,'':'')+1)||'','' value
 11           from input
 12         )
 13       select prefix||'' ''||
 14              substr(value, instr(value,'','',1,line)+1,
 15                            instr(value,'','',1,line+1)-instr(value,'','',1,line)-1)
 16               value
 17       from data, lines'
 18    using str;
 19  end;
 20  /

Procedure created.

SQL> var c refcursor
SQL> set autoprint on
SQL> exec p(:str,:c)

PL/SQL procedure successfully completed.

VALUE
--------------------------------
Blank: 1
Blank: 3
Blank: 17

3 rows selected.