Try this
If([Lead Source] = "Internet", null,
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 0, ToUser("
user@gmail.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 1, ToUser("
sola7@gmail.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 2, ToUser("
lac@gmail.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 3, ToUser("
alyolar@gmail.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 4, ToUser("
pconeo@gmail.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 5, ToUser("
mark@greca.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 6, ToUser("
gary@greeca.com"),
Mod([Record ID#],ToNumber([Number_Of_Reps])) = 7, ToUser("
lj@greeca.com")
)