154

This number is a composite.

154 is the largest maximal gap under 10 million. [Russ]

154 = (1*5*4)*(1+5+4) - π((1*5*4)*(1+5+4)). Note that 154 is the smallest multi-digit number with this property. [Firoozbakht]

(There are 3 curios for this number that have not yet been approved by an editor.)