Actually 19 also can =P
Just alight along Loyang Avenue can le.
Actually ar...there are infinite number of ways, you can either
go direct or you can loop around Woodlands, Changi Airport
or CCK before getting there. So i have no numerical answer to
this question 
Use the All Bus Way:
252 - JKN Stn - Boon Lay Int
172 - Boon Lay Int - CCK Int
925 - CCK Int - Wdl Int
858/168 - Wdl Int - Jln Kayu
39 - Jln Kayu - Tamp Int
29 - Tamp Int - Changi Village Ter.
OR
252 - JKN Stn - Boon Lay Int
241 - Boon Lay Int - Jurong West St 91
99 - Jurong West St 91 - Clementi Int
Turf City Shuttle - Clementi Int - Turf City
Turf City Shuttle - Turf City - Toa Payoh
8 - Toa Payoh - Tamp Int
29 - Tamp Int - Changi Village