We investigate the possible implications of the measured value of the scalar tilt n _ { s } for the tensor-to-scalar ratio r in slow-roll , single-field inflationary models .
The measured value of the tilt satisfies n _ { s } -1 \sim 1 / N _ { * } , where N _ { * } \sim 60 is the number of e -folds for observationally relevant scales .
If this is not a coincidence and the scaling holds for different values of N , it strongly suggests that either r is as big as 10 ^ { -1 } ( a possibility in tension with the recent data ) , or smaller than 10 ^ { -2 } and exponentially dependent on n _ { s } .
A large region of the ( n _ { s } , r ) plane is not compatible with this scaling .