OFFSET
1,1
MATHEMATICA
Select[Flatten@ Array[FromDigits /@ Tuples[{1, 3, 7, 9}, #] &, 3], CompositeQ] (* Michael De Vlieger, Jun 01 2017 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Luke Zieroth, May 26 2017
STATUS
approved