Almost prime

A two-digit number ab is called almost prime if one obtains a two-digit prime number by changing at most one of its digits a and b. (For example, 18 is an almost prime number because 13 is a prime number).

is called almost prime if one obtains a two-digit prime number by changing at most one of its digits  and 

(For example, 18 is an almost prime number because 13 is a prime number).

 References 

Category:Prime numbers
Category:Integer sequences