CREATE OR REPLACE FUNCTION sumfivenumbers ( n1 NUMBER, n2 NUMBER, n3 NUMBER, n4 NUMBER, n5 NUMBER)
RETURN NUMBER
IS
   Sumnums NUMBER;    
BEGIN
     SELECT SUM(n1+n2+n3+n4+n5-1) INTO Sumnums FROM DUAL;      
      DBMS_OUTPUT.PUT_LINE(Sumnums);
RETURN 1;
END sumfivenumbers;
/

SELECT sumfivenumbers(5,5,5,5,5) AS "Five Numbers less 1" FROM DUAL;

SQL> CREATE OR REPLACE FUNCTION sumfivenumbers (n sys.odcinumberlist)
  2  RETURN NUMBER
  3  IS
  4     Sumnums NUMBER;    
  5  BEGIN
  6    Sumnums := 0;
  7    FOR i IN n.FIRST..n.LAST LOOP
  8      Sumnums := Sumnums + n(i);
  9    END LOOP;
 10    Sumnums := Sumnums - 1;
 11    RETURN Sumnums;
 12  END sumfivenumbers;
 13  /

Function created.

SQL> SELECT sumfivenumbers (sys.odcinumberlist(5,5,5,5,5)) AS "Five Numbers less 1" FROM DUAL;
Five Numbers less 1
-------------------
                 24

1 row selected.

SQL> SELECT sum(column_value)-1 AS "Five Numbers less 1" 
  2  FROM table(sys.odcinumberlist(5,5,5,5,5))
  3  /
Five Numbers less 1
-------------------
                 24

1 row selected.

SELECT 5 + 5 + 5 + 5 + 5 - 1 FROM DUAL
/