Question 269078
let the required number be ab

we have a<=4 and b should be 1 or 3 or 7  since it is a prime no. and the sum of the digits is 8 and product 7

so if b=1, a should be 7 but a is <=5

if b=3 then a should be 5 but not possible

if b=7 then a=1 and also their product will be 7


so the answer is 17