#Mathematica, 53 bytes
Mathematica, 53 bytes
!Flatten@Table[Tr/@Tuples[{6,9,20},i],{i,#}]~FreeQ~#&
#Mathematica, 53 bytes
!Flatten@Table[Tr/@Tuples[{6,9,20},i],{i,#}]~FreeQ~#&
Mathematica, 53 bytes
!Flatten@Table[Tr/@Tuples[{6,9,20},i],{i,#}]~FreeQ~#&