Thanks to Chrise and Tevor.
I'm going to attempt to recreate the crossword here. Sometimes once you hit "Add post" it goes a bit skewed.
2 8 letters T _ _ _ _ _ N _
T
?
9 N ? ? ? E ? 6 letters N _ _ _ E _
?
12 R ? ? ? 4 letters R _ _ _
?
17 L O N G D I V I S I O N
?
2D T-trill for repeated 4 (8) 4 is ADDITION
9A 27, for example, but not 19 (6) 27 is ZERO 19 is INFINITY
12A Go from 12 to 13, or 12 to 9? (4) 12 is ????, 13 is ANGLE, 9 is ?