Greek numbers

I was teachng my intro to Greek class about numbers this morning (numbers above 
4 being indeclinable) and one student asked a question I realized I don't know 
the answer to, so I hope someone can help.  In those numbers expressed with a 
number plus a multiple of ten (e.g. treis kai deka), does the treis decline, or 
is it always nominative.  The fact that the number does reflect gender (i.e. 
treis or tria) suggests that it might also show case, but I was not able to 
find an answer in Smyth. 

Prof. Margaret L. Cook
Department of Modern and Classical Languages
Saint John's University & College of Saint Benedict
Collegeville, MN 56321
http://employees.csbsju.edu/MCOOK/

 polÊ te diaf°rein oÈ de> nomEURzein ênyrvpon ényr?pou, krãtiston  d¢ e?nai 
~stiw §n to>w énagkaiotãtoiw paideÊetai. . "All men are created equal; some 
just work harder in the preseason." -- Thucydides 1.84.4