41

This number is a prime.

The product of the digits of 41 is 4, and the sum is 5; hence 4*41+5=169=13^2 and 41 is the 13th prime. Further, 5*41+4=209 and reversing the digits gives 902, add to 209 to get 1111, which is four one's or 41. [Bergot]